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Colm Mulcahy
Mathematician Colm Mulcahy's latest book is Mathematical Card Magic from AK Peters/CRC Press.

He's recently written for Scientific American.

He earned a B.Sc. and M.Sc. from University College Dublin, in his native Ireland, and then a PhD from Cornell University. He's Professor of Mathematics at Spelman College, in Atlanta, Georgia, where he's been teaching since 1988. He's currently on research leave in the DC area.

His mathematical interests are broad, and he is a recipient of the Mathematical Association of America's Allendoerfer Award for excellence in expository writing. He’s been publishing original mathematical card trick principles bi-monthly at since 2004, and other puzzles of his have appeared in the New York Times. He also blogs as "Maths Colm" at Aperiodical and tweets as @CardColm.

He was fortunate to know Martin Gardner for the last decade of his life and is very involved in the Gardner Centennial celebrations currently unveiling.

Entries by Colm Mulcahy

George Boole, One of the Great Unsung Architects of Today's World, Is Unsung No More

(1) Comments | Posted November 2, 2015 | 1:50 PM


Today marks the 200th anniversary of the birth of George Boole, the English logician and mathematician who laid the foundation of the digital age with his pioneering book The Laws of Thought in 1854, published during the 16 years he served...

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학자들이 수학적으로 완벽하게 담배를 쌓기 위해 노력하는 이유

(1) Comments | Posted October 28, 2015 | 1:30 PM

무한히 긴 담배 20개비를 모든 담배가 서로 닿도록 배열할 수 있을까? 휘거나 부러뜨리면 안 된다. 담배들이 닿지 않는 불필요한 부분을 잘라내면 유한한 길이의 담배(원한다면 같은 길이) 한 갑을 포장해서 특이한 기념품으로 팔 수도 있겠다.

수학자들과 엔지니어들은 이게 가능한지 진심으로 궁금해 한다. 2년 전 일곱 개의 무한히 긴 담배나 원통이 서로...

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The Search for the Mathematically Optimal Pack of Cigarettes

(0) Comments | Posted October 21, 2015 | 5:41 PM

Is it possible to arrange 20 infinitely long cigarettes in such a way that each one touches the other 19? No bending or breaking is allowed. Cutting off the unneeded ends--away from the zones where cigarettes touch--we'd have finite cigarettes (of the same length, if desired) which could be packaged...

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John H. Conway: Genius at Play

(2) Comments | Posted July 14, 2015 | 1:11 PM

Genius at Play: the Curious Mind of John Horton Conway (Bloomsbury) by Canadian writer Siobhan Roberts is the new 450-page biography of a remarkable and undeniably eccentric English mathematician who's long been a main attraction at Princeton University.

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Ingenious Mary: Innovative Irish Science Journalist Leaves a Formidable STEM Legacy

(0) Comments | Posted June 19, 2015 | 5:44 PM

The premature death has taken place of Irish journalist Mary Mulvihill, aged 55, after a short illness. Mary was a one-of-a-kind national treasure in science history research and communication across many media platforms as well as in person, and an effective and infectiously enthusiastic community builder whose professional...

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Myles Away From Mathematics, Magic and Mystery

(3) Comments | Posted May 22, 2015 | 11:28 AM

Did you ever wish you'd asked one more question of somebody you once knew, who is no longer around to chat with?

CAPTION: Martin Gardner and Brian O'Nolan, early...
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Mathematical (and Poetic) Offerings From the Land of Saints and Scholars

(1) Comments | Posted March 23, 2015 | 5:34 PM

With another St Patrick's Day safely behind us, it's a good time to remember that over the past few centuries The Land of Saints and Scholars has made significant -- if sometimes overlooked -- contributions to mathematics, science and engineering, as well as to the arts. Ingenious Ireland's...

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Top 10 Martin Gardner Books (This List Goes Up to 11)

(0) Comments | Posted October 28, 2014 | 6:51 PM

"Pick up anything Martin Gardner wrote," advises mathematician, magician and MacArthur award winner Persi Diaconis. "You'll smile and learn something." This is very true, but with over 100 books to choose from, by Gardner's own estimation, where should one start?

The Top 10 list below (which actually goes...

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You Don't Have to Be a Genius to Work at Subway...

(0) Comments | Posted September 18, 2014 | 11:51 PM

...but 59-year-old mathematician Yitang "Tom" Zhang is now living proof that a former Subway worker can be an official genius: He's one of the winners of the 2014 MacArthur Genius Grant. Curiously, five of this year's 21 awardees used mathematics or statistics in their work.

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Mathematics, Magic and Mystery

(1) Comments | Posted April 30, 2014 | 9:10 PM

Mathematics is all about numbers and number crunching, right? Actually, no, only part of it is. (In general, number crunching is more accurately identified with the domains of business, accountancy or engineering.)

Mathematics is more about curiosity, logic, patterns and beauty, and also has its share of delicious surprise, wonder,...

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Magical History Tour -- and Your Fave Fab Four Album Is in the Cards

(0) Comments | Posted February 7, 2014 | 3:11 PM


Main Entry Image

Paul McCartney, George Harrison, John Lennon (vorne v.l.) und Ringo Starr (hinten) von der englischen Band The Beatles treten in New York, USA, in der TV-Sendung "Ed...

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Martin Gardner -- The Best Friend Mathematics Ever Had

(21) Comments | Posted October 20, 2013 | 8:18 PM


What do L. Ron Hubbard, H.G. Wells, G.K. Chesterton, Lord Dunsany, Alice in Wonderland, M.C. Escher, John H. Conway, Roger Penrose and Oprah Winfrey have in common? The same thing as Isaac Asimov, Vladimir Nabokov, and Salvador Dali. And the vase illusion shown, which was designed...

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Getting Kids Excited About Mathematics, One Festival at a Time

(0) Comments | Posted July 11, 2013 | 5:00 PM

It was a beautiful May morning, and McCaw Hall in the Arrillaga Alumni Center at Stanford University was jam packed and buzzing with excitement. About 250 youngsters aged 7 to 17 had come in search of challenges and thrills, and they weren't disappointed by the festive atmosphere and friendly vibe.

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What Do I Have to Do to Get an A in This Class? (A Mathematical Perspective)

(1) Comments | Posted April 30, 2013 | 7:07 PM

It's that time of the year again. Final exams in colleges and universities are getting close, and one of the most popular questions students are asking their instructors is, "What do I have to do to get an A in this class?" (In other cases it may be, "What do...

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Centenary of Mathematician Paul Erdős -- Source of Bacon Number Concept

(0) Comments | Posted March 26, 2013 | 12:04 PM

In recent years many people have had fun attributing Bacon numbers to actors, reflecting how far removed from working with Kevin Bacon they are. Edward Asner has Bacon number 1 as he made a movie with Bacon, and Elvis Presley had Bacon number 2 (having been in an...

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In My Heart of Hearts: Valentine's Day Special

(0) Comments | Posted February 14, 2013 | 9:14 AM

Just in time for Valentine's Day, a magical romantic experience for all lovers (of cards), thanks to the power of mathematics.

Take out a deck of cards and extract the thirteen Hearts, setting the rest aside. Deal the Hearts into a heart-shaped display, something like as shown. There is no...

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The Role of Biking and Hiking in Mathematics

(3) Comments | Posted February 1, 2013 | 11:00 AM

In my last post, I discussed the less-obvious role of mathematics in answering simple questions about biking. What about the role of biking (or hiking) in answering difficult questions about mathematics?

Many people who run, hike or bike long distances have noticed that these activities...

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Mean Questions With Harmonious Answers

(3) Comments | Posted January 18, 2013 | 6:20 PM

2013-01-15-TucsonCU.jpgAodh and Bea each biked half of a 180-kilometer fundraiser race, in that order, as a relay team. His average speed was 36 kilometers per hour, and hers was 20 kilometers per hour. What was their average speed overall?

They shared the task...

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A Pound of Quarters vs. a Pound of Dimes: Which Is Heavier, and Which Is Worth More?

(9) Comments | Posted January 2, 2013 | 1:38 PM

2012-12-28-Balance2.jpgMany youngsters have heard, and perhaps even fallen for, the classic teaser: "Which is heavier: a ton of bricks or a ton of feathers?"

The juxstaposition of the words "brick" and "feather," in the context of weight, serves as perfect misdirection. It catches a...

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Flipping Miracles (or Bar Bets to Amaze Your Friends)

(6) Comments | Posted December 14, 2012 | 6:30 PM

Do you like a little cream in your coffee, or are you one of those people who likes a little coffee in your cream?

In front of you is a pot of coffee and a jug of cream.


You transfer one teaspoon...

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