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Theorem of the Day is maintained by Robin Whitty. Comments or suggestions are welcomed by me.
"Theorem of the Day" is registered as a UK Trademark, no. 00003123351. All text and images and associated .pdf files © Robin Whitty, 2005–2022, except where otherwise acknowledged. See FAQ for more.
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Posted by Dennis Claudio04:09, 12 08 2022Richmond, CA USA
I used to visit regularly a number of years ago to download the theorems. Compiled them into an indexed pdf file. Gave a couple of printed copies to some high school students forming a math/science club. Had hopes of seeing more math related projects in the local science fairs. Just the last few days I've been able to re-visit. A favorite.

Posted by Norio Kosaka14:52, 10 04 2022Japan
What a wonderful site!

Posted by Richard M. Low08:02, 07 03 2022San Jose State University, USA
A beautiful website! Keep up the great work! Have you ever consider collecting all of "Theorem of the Day" webpages and making a book to sell? I would certainly buy such a resource.

Posted by Sachal Abdulah18:19, 25 01 2022Charles University, Czech Republic
A perfect place to feed my mind's appetite.

Posted by Paul Uhlig17:41, 25 09 2021St. Mary's Univ. in SA TX USA
This is a great resource! Thank you for all the work putting this together, and to all the mathematicians upon whose shoulders we stand.

Posted by Ryan S15:51, 03 09 2021Canada
Awesome. Flex that brain!

Posted by Matthias Kawski07:20, 13 04
What a wonderful site!

found you via parking functions,
a particularly beautiful page


Posted by Manish Khare08:33, 07 01 2021MIT Academy of Engineering, India
I wish to speak about a method, which I claim, to be a solution of Goldbach Conjecture..

Posted by Dongjai Lee14:45, 16 12 2020Greenville, SC, USA
Fun place to visit!
I wish you explain these topics through Youtube like Mathologer

Posted by Peter Neupert18:51, 24 07 2020Germany
Special interest in algebraic number theory, complex analysis and noneuclidian geometry I fully appreciate your excellent website. Thank you and best regards

Posted by The Polytopologist21:47, 07 05 2020Kalamazoo
When you waste time, you murder success.

Posted by John the Scott18:40, 03 05 2020Dallas, Texas, USA
just learned of this site and Lothaire!

Posted by Quinn09:51, 27 04 2020USA

Posted by Justin08:48, 04 12 2019
This website truly is fantastic and a great read to start everyday, thank you so much for maintaining it.

Posted by Juju Schenzinger19:18, 27 09 2019
I learned of this website in a lecture given by Prof. Raymond Flood, of Gresham College. Thank you for maintaining this site, it is most definitely appreciated by folks like me: stuck at home and doing my studies online.

Posted by Dino Calvisi07:27, 20 09 2019Sydney, Australia
Excellent website.Great amount of information. Thank you, Dino Calvisi

Posted by Sam Nejad06:42, 27 04 2019Western Australia
Great site with comprehensive PDFs.
Your work is appreciated far & wide.
Regards, Sam Nejad.

Posted by Sam Nejad06:40, 27 04 2019Western Australia
Excellent! Finally a clearly laid out site with great, comprehensive PDFs.
Thank you for all your efforts. You are appreciated far & wide...
Regards, Sam Nejad.

Posted by Priyal Kumar13:30, 12 02 2019India
Hello people

This site is the reason that now I love Maths very much. I want to extremely thanks to those who made the list of a lot of theorems.

Posted by Simon Betron16:07, 29 11 2018Chapel Hill, NC, USA
Hi, my name is Simon, and I love math. From a young age, I've found solace in the beauty of numbers. Nothing brings me more joy than uncovering the hidden patterns described with numbers and watching them weave into mathematical abstractions. If I had to choose a favorite number, I think it would be 4. It's a really good one. Please post more content using the number 4. Love you!
Thanks and regards,
Simon C. Bertron

Many thanks to Theorem of the Day, and the peoples behind it. I've learned and questioned my knowledge of maths. Besides the historic facts and the life of great mathematicians.

Posted by navneeth15:31, 17 08 2018japan
As an applied researcher, this really expands my knowledge of mathematics. I am constantly on the lookout for new theorems to apply in real world formulations. This is a treasure trove. Please continue to educate us.

Posted by Kyle21:57, 10 08 2018Chicago
As an aspiring Math major, your site really provides an incredible depth!

Posted by Candy Elliott buzzelli03:56, 13 04
Thank you !

Posted by Doni02:48, 25 03 2018
The internet is wonderful because I found this blog with a lot of interesting information about math.

Posted by Avijit15:42, 29 12 2017
Great resource. Very entertaining. Have a Happy New Year!

Posted by J.J.09:54, 10 09 2017Auckland, New Zealand
Excellent website! Thank you

Posted by William15:29, 04 08
Great website to learn more about Theorems! Will blog about this in my math website.

Posted by Remy15:19, 26 12

Could you add RSS feed to your pages? This way, I can be notified when a new theorem is there.

best regards


Posted by jojo17:59, 28 11 2016Austin, TX
This is an awesome website! Love the conciseness.

Posted by SMD04:04, 28 11 2016Greece
I thought it was a great idea, until I read the proofs of two theorems. I mean,really? You violated the beauty of Euler's identity and Stirling's formula by using tau over pi.

This is ridiculous, preposterous and unacceptable. Use pi. Shame on you for promoting tau.

Tau is a muon, a subatomic particle in Physics. It's not a mathematical constant, no matter how much you promote it.

I mean even the symbol is ridiculous. You could have used pi-star, as an analogy to h-bar. In this way it would show the connection to the fundamental constant pi, as h-bar shows the connection to Plank's constant h.

Posted by Salman Aslam15:05, 15 02 2016LUMS, Pakistan
Great job. Keep up the great work!! All the best.

Posted by Sam00:30, 10 10 2015CMU
Thank you for the Erdos-Ko-Rado theorem!

Posted by Zach06:20, 19 08 2015Boston, MA
Amazing site! You should aim to include Gershgorin's Theorem! It's rather visual.

Posted by Pedro20:37, 15 08 2015Peru
I just wanted to send this message for saying THANKS for maintaining this interesting and curious website! All the best!

Posted by crono03:45, 17 06 2015México
Amazing work! Mostly the thing I would do in a work like this.

Posted by embossitworld11:50, 16 06 2015embossitworld
Hello, I have browsed most of your posts. This post is probably where I got the most useful information for my research. Thanks for posting, maybe we can see more on this. Are you aware of any other websites on this subject.

Posted by Bob lalas08:32, 23 06
I thing this site is doing some new and interesting things. Keep it up.

Posted by gopal17:56, 15 06 2014india
amazing page
i love maths.

I love ur jobs very much..keep ur good job :)

Posted by Douglas Hainline07:03, 23 04 2014UK
Thanks for a wonderful site! This should be more widely known.

Posted by dobry09:24, 19 04 2014
I like youre website, it's very helpfull
please revisit also mine

Posted by Edier Castaneda20:50, 20 08 2013universidad catolica de oriente
wonderful page

Posted by Dan Bromberg16:40, 29 04 2013
You should add the difficult to prove but easy to understand "Steiner Lehmus" Theorem.

Posted by Aperna Deb16:26, 15 10 2012India
Awesome! But where are the proofs?

Posted by Edmund21:27, 09 10 2012London
Love the idea and the website.

Posted by Anamika08:06, 18 02
Good website with great content.

Posted by Paul Chernoff12:07, 15 12 2011U.C. Berkeley
Re the list of theorems by women mathematicians: where is Marina Ratner,
Michelle Vergne, Jenny Harrison, etc etc?
(Of course many women mathematicians, for
example Ratner, consider themselves mathematicians, period.)

Posted by Peter H.23:08, 10 12 2011
Great Website, helps me to refresh my Math knowledge. Keeps my brain in training. Thank you very much.

Posted by Oliver18:42, 28 11 2011Germany
It is a great website
thank you for sharing

Posted by bottes timberland06:56, 26 11
Many thanks to the person who made this post, this was very informative for me. Please continue this awesome work. Sincerely...

Posted by Mandie Sullivan12:12, 07 11 2011Cursos de Cocina en Barcelona
Great job! Hours looking for resources and you had all of this here!

Posted by Cursos de cocina en Barcelona09:42, 30 10
I just want to acknowledge the enormous and fantastic work you do every day. I am very happy to participate in it. Mandie

Posted by T Russell23:49, 10 08 2011Texas, USA
I must say, this website has made my day. I am SO glad I found out about this. It is now my homepage :)

Posted by AGT STUDENT00:54, 14 04 2011QMUL
great website sir!! you help make the world a mathematically beautiful place!!

Posted by Cleveland Web Design10:27, 05 04
Great work

Posted by Aakriti13:24, 03 03 2011India
Great work!! Love it :)

Posted by frwe11:56, 18 02 2011
Thanks you.

Posted by R Glen Cooper, PhD03:23, 22 01 2011British Columbia, Canada
Awesome site - congratulations! You've made mathematics compelling.

Posted by Fio 19:59, 21 01 2011Stuttgart, Germany
This website is awesome! I only wish my English was better...

Posted by Gerard P. Michon, Ph.D.14:13, 21 12
Back in 2005, when he started this site, Robin Whitty set out for himself a goal of 366 theorems; one per day for an entire [leap] year! The next theorem will be number 183. This is the halfway mark!

Congratulations for this great achievement, Robin. Only 183 to go!

Gerard Michon, curator of the Numericana Hall of Fame:

Posted by Bramma13:05, 16 12 2010Bharathidasan Univesity
amazing web site.

Posted by Jane Clare Pawling10:27, 10 12 2010United States of America
Hello, I am glad to be able to visit here.

Posted by stephane berrebi14:12, 13 11
Wonderful idea, terrific work that could easily become a popular math encyclopedia of reference with some sponsoring and editing !

Posted by Sandra Deckard11:42, 12 10
I really liked your blog!

Posted by la reference en vente privee21:37, 04 10
Quite an original idea, but why not the proverb of the day ?

Posted by Morgan 11:19, 04 10 2010Paris
Thanks for this website, it reminds me my school studies in engineer school :) by Morgan

Posted by Mutine09:29, 04 10 2010france
I really enjoy Math, thank you for you work.

Posted by Marphisa 17:20, 03 10
Great job.
The web-site is wonderful and also shows your excitement with regard to what you do.

Posted by Richard M. Low21:57, 13 08 2010San Jose State University, CA, USA
This is an excellent website and mathematical resource. Keep up the great work!

Posted by marcia07:59, 11 08 2010australia
Please find out about your leaders and crimes going on all over the world for ten years now against human rights in general. The own government, in full democracy, is enslaving people, stealing their intelligence, literally, amongst others, you won't believe it. I have proofs exposed of several crimes on my websites. More than 400,000 dead so far gratuitously. I am a victim myself, need your help, am victim since end of 2001, currently slaved. Biotechnology, USA. Please visit hubpages (it is a .com), see profile/MARIAMORTA there to get an idea. The site 'how you can help' brings explanation on what to do. Very little can be done, but reckon it is all there. Rush. Spreading to others already is some help, figures may bring justice, finally, some item of the page 'how you can help' done. Pls rush.

Posted by Jamie Simpson05:50, 11 08 2010Curtin University, Australia
Good stuff!

Posted by Nils Wiegner10:03, 15 06 2010
Thanks for all the information you share with us. It's always a charme to read everything you post in here.

Posted by Hicham YAMOUL09:34, 25 05 2010
It will very interesting to build the analogous theorem of Van Kampan theorem for the nth homotopy groups, so it will be easy to calculate them.

Posted by Audrey01:28, 14 05 2010USA TX
Great site

Posted by Gérard P. Michon16:11, 08 04
It was a nice surprise to find the 10-year anniversary of Numericana mentioned prominently on the front page of "Theorem of the Day"... Thanks, Robin.

It's always great to visit this superbly crafted site. The halfway mark (183 theorems) is approaching rapidly... THAT will be a nice cause for celebration!

Posted by Gaurav Bhatnagar15:31, 04 04
Great site. Thanks.

Posted by Paul Murray02:25, 30 11 2009Cold Hard Truth
nothing quite like the challenge within the mind :)

Posted by Hypnosis Johan02:23, 30 11 2009Australia
love your effort robin, top site that is great value.

Posted by Josh08:37, 29 11 2009UK
I recently bought an A level maths book to try and brush up on the maths I've forgotten since my college days. Its thank's to this site I got back into maths in the first place.

Many thanks!

Posted by Jay00:27, 28 08 2009Chicago
I have been fooling with math too. I really love it. Memorizing binary code and numbers are what I'm into now

Posted by Noelle20:20, 19 08
Do you email the Theorem of the Day.
Please add me to your list - thanks.

Posted by John10:48, 16 07 2009Isle of Man
Yes, Congrats guys!

Posted by Bill Oswald04:06, 16 07 2009Hollywood, USA
Big Congratulations and Mahalo on the Women's Theorems 2009 Calendar. Will anyone agree with me that the classic Konigsburg Bridge problem reduces to solving 3 equations in 2 unknowns?? Thank you for input.

Posted by Bob14:57, 30 06 2009Italy
Maths is my passion also!

Posted by John12:53, 30 06 2009UK
This has also resparked my interest in Maths. I love it - many thanks!

Posted by Ronstewart06:45, 23 06 2009Australia
There is no simple algebraic formula for the catenary_

Posted by Josh22:57, 17 06
This has resparked my interest in Maths. Love it - many thanks!

Posted by Rupinder Dulay09:48, 12 05 2009CDHS Castle Douglas
A great site even though I find the mathematics very difficult but the real mathematician I work with are using the calendar with their A level students.

Posted by Imelda Almqvist19:42, 15 04
Dear Robin, your website is such a treasure trove of mathematical ideas - I will keep on coming back for more!!

Had some fun today with the Borsuk-Ulam Theorem. The ingredients were a tailor's tape measure, a ruler and a 'mathematical balloon' (on which I had scribbled numbers). And you know, I did find number correspondences!

The real challenge will of course be to express some of my findings in a painting...

With many thanks for feeding me a diet of mathematical concepts! :-)

Imelda Almqvist

Posted by Candida17:08, 12 04 2009Circle appreciation
Oooh I just love todays theorem! Very harmonious! Keep up the excellent imagery for a simples way to success Mr.Whitty!

Posted by Candida16:54, 27 02 2009cloud 5
Absolutely love todays theorem!! Pretty, colourful, intriguing and full of suprises! Happy Birthday to Ms. Sidhu today too! Keep up the good work! x

Posted by Hyeong-Kwan Ju06:22, 23 02 2009Chonnam National University, S. Korea
Very glad to meet Website like this.
Hope this is one giant step to let people outside of mathematical world
know what we are doing and concerning
It is very useful for the mathematician
to know the other side of mathematical world.

Posted by Des Wann22:31, 05 01 2009Australia
What a wonderful site for a retired Head of Mathematics Department! Keeps up my interest in both the history and content of mathematics. It also brings back many memories (both good and bad) dealing with the subtle nuances of the subject.
Well done, Robin.

Posted by Willy Hereman23:06, 15 12 2008
Thank you very much for offering this site and also for the free calendar. Beautiful!

Posted by Gérard P. Michon, Ph.D.02:50, 11 12
Your 2009 calendar is beautiful. Thank you so much for producing it.

Posted by mike newman01:27, 26 11 2008ottawa
Hey you are number one on google!

Posted by terence tao20:36, 10 11 2008ucla
I want to congratulate you on your beautiful site. may you reach 1000 theorems one day.

Posted by emri19:41, 04 11 2008vendi
keep up the good work!

Posted by carrie13:29, 02 11 2008hackney
CRB's 25th?

Posted by John Kemeny21:08, 21 10
Very nice!

Posted by Harriet Pollatsek22:35, 18 10 2008Mount Holyoke College, South Hadley, MA, USA
Greetings from New England to Old England.

Posted by Kalun13:27, 17 10 2008CEIBS, Shanghai, China
My students never had so much fun with maths before. Well done, keep up the good work.

Posted by Harvey16:42, 03 10 2008Canada
A very nice site, Robin. It is attractive and informative. A great contribution to the popularization of mathematics.

Posted by jaejun17:36, 04 09 2008london
hi do you remember me??
I'm korean we met near the new cross gate before 10 days.
your homepage is really intereting..
I'm not sure whether you see or not but, I'll just try
have a good day

Posted by Sam tetruashvili16:57, 24 05 2008Carnegie Mellon University, School of Computer Science
Great site.

Posted by Andy Drucker17:50, 23 05 2008MIT, Massachusetts (grad student, EECS dept)
Beautiful site! I'll tell my friends.

Posted by Eileen08:05, 23 05
an excellent site, keep up the good work!

Posted by Kungwa14:58, 01 05 2008King's College London
I would like to reiterate the semi-recluse, Charles Wallingford's posting. Keep up the good work

Posted by Norman12:48, 01 05 2008Queen Mary Univ London
Great site - keep up the good work

Posted by ahmad15:18, 18 04
your site is nice
may be i will list it in the mathsite glossary
in our site

Posted by Candida Bradley08:57, 07 04 2008Salford University
What a delight the cows are today!! ooooh so pretty :)

Keep up the good visuals as well as the intriguing maths!

Posted by Carrie Rutherford15:39, 12 03 2008LSBU
Well, here I am. As you know, I think theorem of the day is GREAT, and I have spread the calendars far and wide.

Posted by Gagan12:52, 06 03 2008London
Congratulations on the calendar and spreading the word on theorems. Look forward to you next batch of theorem calendars

Posted by Candida11:28, 27 02 2008Salford University
Thank you for brigthening up my days with your beautifully-drawn and colourful theorems! They make maths seem approachable, even to those who scraped through their maths GCSE. Continue to delight!

Posted by Fatima Affif Chaouche09:30, 26 02 2008University of Sciences and Technology Houari Boumediene. Algiers. Algeria.
Certainly I am happy to have the opportunity to transmit you my congratulation! Also to thanks you for giving me the possibility to discover this web site, which is really a very important site. Happy that I am in your mailing list.
Hope to receive more and more news.

Posted by mike newman00:15, 25 02 2008Victoria University Wellington, New Zealand
Congratulations! Happy century, TotD.

Posted by Taoyang20:58, 24 02 2008London
Congratulations Robin in building the century and Tony in creating the century:-)

Posted by Dave07:35, 22 02 2008Durham
Keep up the good work!

Posted by Stuart J Hutcheon18:45, 21 02 2008London South Bank University
Congratulations Robin in reaching your century. Well done.

Posted by sara munday15:42, 21 02
Congratulations on your 100 theorems! Slightly belatedly, many thanks for the calendar of theorems by women mathematicians. It is an inspiration every day.

Posted by Cahit15:28, 21 02
Remarkable achievement. Hope to see other 100 theorems soon.

Posted by Jean Drabbe07:53, 20 02 2008University of Brussels
I was told about Theorem of the Day be
a colleague. I am delighted he did.
Congratulations !!!
Jean Drabbe
University of Brussels

Posted by Tony Forbes20:38, 19 02
Hi Robin,

Congratulations on reaching that magic number! And how appropriate to celebrate the historic occasion of Theorem 100 with a mathematical object containing word 'century' in its description.

Keep up the good work!

Best wishes,


Posted by John16:37, 19 02 2008London
The calendar looks cool!

Posted by Pinky15:14, 19 02 2008London
As a non-mathematician, I can only appreciate the theorems from an aesthetic point of view - but love the links to artwork too!

Posted by Charles Wallingford15:03, 19 02 2008Donostia
Keep up the good work!