Card Colm

Colm Mulcahy is Professor Emeritus of Mathematics at Spelman College, Atlanta, GA, where he taught between 1988 and 2020. He served as chair of the department 2003-06.

"Mathematics may be presented in polished logical form, but it's discovered and mastered in a totally different, sometimes semi-haphazard way, with plenty of false turns, dead ends and much frustration and self-doubt."

He's always reachable on email.

He is Chair of the Gathering 4 Gardner, which is currently hosting 52 online presentations per year on mathematics, puzzles, magic and more (see the resulting videos).

This 2017 interview done in Belgrade, Serbia, reveals a lot about what makes him tick as a mathematician and teacher.

Read his review of The Unity of Combinatorics by Dub Brown & Richard Guy (co-written with Neil Calkin).

Read his Guardian obituaries of John H Conway and Ron Graham.

Colm's musings (and puzzles and photos) have been featured at RTE, the Guardian, and BBC, and the NYT.

He has been translated into Korean, Japanese, Mandarin, Cantonese, Polish, French, Spanish, Finnish and Serbian. But not Irish (fós).

He is the creator and curator of the Annals of Irish Mathematics & Mathematicians (see overview, and the associated monthly blogs).

He is also the creator and curator of SpelMath, which documents the history of mathematics at Spelman College going back over a century.

MoMath Math Encounters — Online 6 May 2020 ("Mathemagic with a Deck of Cards" with Colm Mulcahy) ["Your Math Encounters video is really good. It is one of the best MoMath presentations that I have seen. Your slides were excellent (the Proof Without Words shuffling cards slide was really nice). You are a good teacher." BB]

NUIG Seminar Thur 28 May 2020 ("One, Two, Many (or a dozen reasons why mathematics isn't as easy as 1, 2, 3)").

UGA SUMR Conference 2020 Sun 2 Aug 2020 ("One, Two, Many (or a dozen reasons why mathematics isn't as easy as 1, 2, 3)").

His proudest contribution to the OEIS is here.

Colm with Erdos

Paul Erdős (1913-1996) visited Spelman in the spring of 1989. He spoke at the Pi Mu Epsilon induction banquet. See Colm's Huff Post article (in which the year of that visit is listed incorrectly).

At that point, Colm's Erdős number was probably 4. Decades later, thanks to a collaboration with Neil Calkin, it dropped to 2.

Colm with JHC'

John H. Conway (1937-2020) was sometimes described as magical. He enjoyed playing with the anti-gravity decks of cards, at MOVES conference at MoMath in NYC, August 2017. (Photo courtesy of Ibrahim Dulijan.)

Read Colm's Guardian obituary of JHC and watch his video tribute. Or about John's 1995 Spelman visit or two wonderful triangle facts which he helped to clarify.


(Jul 2021, invited) "The Scottish Irish Mathematical Trail", People, Places, Practices: Joint BSHM-CSHPM/SCHPM Conference, University of St Andrews, 12-14 Jul 2021 (moved from 2020).

(23 Jul 2020) "1920-2020: A Century of Mathematics at Spelman College" (video and slides links).

(6 May 2020) MoMath Math Encounters — Online: "Mathemagic with a Deck of Cards" (video on YT).

(24 Jan 2020) "Faculty Excellence at Spelman College" (spring 2018 interview starts on page 12 of the PDF)

(20 Jan 2020) "Reflections of Retired UCC Mathematicians", Irish Math. Soc. Bulletin.

Five all-new presentations were given in 2019:

(invited) "One, Two, Many (or a dozen reasons why mathematics isn’t as easy as 1,2,3)" - EPaDel MAA Section Meeting, Wilkes Barre PA (23 Mar 2019).

"Wait Wait Don't Tell Me" MoMath MOVES, NYC (6 Aug 2019).

(minicourse) "Mathematical Card Magic" MAA MathFest, Cincinnati, OH (1 & 2 Aug 2019).

"Robert Curtis" Gerard Manley Hopkins Festival, Kildare, Ireland (23 Jul 2019).

"Myles Away From Mathematics?" Palimpsests: Flann O'Brien, Dublin 2019, UCD, Dublin (18 Jul 2019).

"Early Maths People at Catholic University and UCD", UCD (13 Jun 2019)

"Galway Travelling Studentship Winners" NUIG (30 May, 2019)

"One, Two, Many (or a dozen reasons why mathematics isn’t as easy as 1,2,3)" Maynooth University (22 May 2019)

Other resources:

Colm's Math Teachers Circle page has a wealth of resources. So does his Maths Week Ireland page.

Mad Math at Smith College Oct 2018 page.

Card Colm's Highlands Maths Treats Jan 2018 page.

Latest articles.

Latest appearances

Spelman Connection 18 Dec 2017

At Áras an Uachtaráin, 17 Mar 2017

Irish President Michael D. Higgins hosts event to mark contribution of science, at which a team of innovative educators from CALMAST and Maths Week were honoured.

The Best Writing on Mathematics 2015
(Princeton, Jan 2016), includes "Let the Games
Continue" by Colm Mulcahy and Dana Richards

"Colm Mulcahy and Dana Richards express their
appreciation and reflections of the significant work
of icon Martin Gardner."

Spelman Press Release

The Mathematics of Various Entertaining Subjects: Research in Recreational Math (Princeton, Dec 2015), includes "Gallia Est Omnis Divisa in Partes Quattuor" by Neil Calkin and Colm Mulcahy

A consequence of this collaboration is that Colm's Erdös number has been halved, from 4 to 2.


30 mins video of 26 Jun 202l talk on "Pioneering WIMEN" from the 3-speaker Women in STEM session at the 9th Robert Boyle Summer School (Colm's part starts half-way in):

30 mins video of 30 Oct 2020 "Iontas Sorcoireach: Cylindrical Surprise" presentation in Irish on "Pioneering WIMEN" for Math Week Ireland

30 mins video of 14 Oct 2020 "Cleas Cárta Matamaiticiúil" presentation in Irish on "Pioneering WIMEN" for Math Week Ireland

82 mins video of 6 May 2020 MoMath presentation Math Encounters — Online: "Mathemagic with a Deck of Cards":

19 mins Serbian video of interview (May 2017), including performance of the Fitch Cheney Five Card Trick with Colin Wright:

3.5 mins Gathering 4 Gardner video of Richard Guy 100th birthday tribute song (Sep 2016):

8 mins Numberfile video on my Little Fibs creation (Jun 2016):

Additional 8 mins Numberfile video on my Little Fibs creation (Jun 2016):

4 mins Matt Parker video on my Low Down Triple Dealing creation (May 2016):

George Boole Song & long video (Maths Week Ireland, 8 mins), 2 Nov 2015:

George Boole Song & long short video (Maths Week Ireland, 6 mins), 26 Oct 2015:

Martin Gardner 101 (Google Tech Talk, 53 mins), 30 Jul 2015:

Martin Gardner 1914-2010 (G4G, 9 mins), 21 Oct 2014:

Interview about book (3 mins), 13 Aug 2013:


South Gwinnett HS Celebration of Mind Tue 12 Dec 2017, 3-6pm.

Intown Atlanta Math Teachers Circle meet-up Sun 29 Oct 2017 at Emory University.

Celebration of Mind Sat 21 Oct 2017.

Maths Week at Mallow, Cork, Ireland, Sun Oct 15, 2017 (all day fair)

Maths Week at Stephens Green, Dublin, Ireland, Sat Oct 14, 2017 (all day fair)

(early) Maths Week "Pioneering Women in Irish Mathematics", ADB-1020, NUIG, Galway, Ireland, 3pm, Fri Oct 13, 2017

(early) Maths Week on Inis Meáin, Aran Islands, Galway, Ireland, Thu Oct 12, 2017

(early) Maths Week on Inis Mór, Aran Islands, Galway, Ireland, Wed Oct 11, 2017

(early) Maths Week at Gairmscoil Mhic Diarmada on Arranmore island, Donegal, Ireland, 9am to 1pm, Tue Oct 10, 2017 (five 40-minute sessions)

Berry College, McAllister Hall 100, Rome, GA, 6:00pm, Mon Sep 18, 2017

EUMMA, Emory University, Atlanta, GA, 6:00pm Thu Sep 7, 2017

MOVES, NY, NY, 1:15pm Mon Aug 7, 2017

MOVES, NY, NY, 3:25pm Mon Aug 7, 2017

"The Library of Irish Mathematics", MAA Mathfest, Chicago, IL, 9:30am Thu 27 Jul 2017, in Salon C8

"Mathemagic with a Deck of Cards," Sligo IT, 4pm Mon, 13 Jun 2017

"A century of NUI travelling studentships: the UCD story," UCD Maths Dept, Dublin, Wed, 31 May 2017

May Month of Mathematics, Belgrade, Mon-Wed, 15-17 May 2017


        ("How a 19th century Irish mathematician helped NASA into space" RTE Brainstorm, 16 Oct 2019)

        ("Hamilton's Ireland" (game), 13 Oct 2019)

        ("Dublin's Mathematical Marsh's", Sep 2019)

        ("Doing the math: in praise of Hamilton and quaternions" RTE Brainstorm, 16 Oct 2018)

        ("Sheila Power (later Tinney), Pioneering Irish Mathematical Physicist", Jan 2018)

        ("", 18 Oct 2017)

        Irish Times ("Peter Lynch honoured for raising awareness of maths", 18 Oct 2017)

        RTE Brainstorm ("A Maths Week salute to some of Irish women who lead the way when it came to a career in mathematics", 18 Oct 2017)

        Donegal Now ("Maths professor with amazing card tricks visiting Arranmore for Maths Week", Oct 2017)

        Maths Ireland ("Pipeline to Pasadena: the Caltech Connection", Sep 2017)

        WIT News ("Pioneering Women in Mathematics in Ireland", Mar 2017)

        AMS Notices ("The Mathematics Genealogy Project comes of age at 21", May 2017)

        WIT News ("Pioneering Women in Mathematics in Ireland", Mar 2017)

        A Century of Mathematical Excellence at Spelman College (JMM talk slides, Woodruff Library Digital Commons, Jan 2017)

        IMS Bulletin (Peter Lynch's "That's Maths" review by Colm Mulcahy, Number 78, No 2, pages 96-99, Dec 2016)

        MAA's Math Horizons (Ken Ono's "My Search for Ramanujan: How I Learned to Count" review by Colm Mulcahy, Vol 24, No 2, page 26, Nov 2016)

        Richard K Guy turns 100 (MAA blog, Sep 2016)

        8 mins Numberfile video on my Little Fibs creation (Jun 2016)

        Additional 8 mins Numberfile video on my Little Fibs creation (Jun 2016)

        4 mins Matt Parker video on my Low Down Triple Dealing creation (May 2016)

        Spelman students write verse and more about Cal III and Real Variables: Spelman's Got (Math) Talent (May 2016)

        A Math Genius Like No Other Comes to the Big Screen (Scientific American, Apr 2016)

        The Best Writing on Mathematics 2015 (Princeton University Press, Jan 2016)

        "Gallia Est Omnis Divisa in Partes Quattuor" (with Neil Calkin) in The Mathematics of Various Entertaining Subjects: Research in Recreational Math (Princeton University Press, Dec 2015)

        George Boole, One of the Great Unsung Architects of Today's World, Is Unsung No More (Huffington Post, Nov 2015)

        The Bicentennial of George Boole, the Man Who Laid the Foundations of the Digital Age (Scientific American, Nov 2015)

        The Mathematical Surprises of Triangles, Squares and Pentagons (Scientific American, Oct 2015)

        Martin Gardner 1914 2010—The Best Friend Mathematics Ever Had (YouTube, Oct 2014-2015)

        The Search for the Mathematically Optimal Pack of Cigarettes (Huffington Post, Oct 2015), also 학자들이 수학적으로 완벽하게 담배를 쌓기 위해 노력하는 이유 (in Korean)

        Given any Delta, there exists Epsilon (Aperiodical, Aug 2015)

        How to Get to the Fourth Dimension (Scientific American, Jul 2015)

        MacTutor History of Mathematics website creators honoured by LMS (Aperiodical, Jul 2015)

        John H. Conway: Genius at Play (Huffington Post, Jul 2015)

        Ingenious Mary: Innovative Irish Science Journalist Leaves a Formidable STEM Legacy (Huffington Post, Jun 2015)

        Myles Away From Mathematics, Magic and Mystery (Huffington Post, May 2015)

        Inteview about George Boole etc (GeorgeBoole200 newsletter, Apr 2015)

        John Conway Reminiscences about Dr. Matrix and Bourbaki (Scientific American, Apr 2015)

        Eight Easy Pieces (you can touch but don’t look) (Aperiodical, Mar 2015)

        Mathematical (and Poetic) Offerings From the Land of Saints and Scholars (Huffington Post, Mar 2015)

        How Many Digits of Pi Do You Really Need to Know? (Scientific American, Mar 2015)

        St Rose's (Belfast, Mar 2015)

        Mathemagic with Cards video (Derby, Feb 2015)

        The Joe Duffy Show (Dundalk FM, 18 Feb 2015, 24 mins)

        MAA's Math Horizons (Mathematical Card Magic: Fifty-Two New Effects book review by Rob Eby, Vol 22, No 2, page 28, Nov 2014)

        MAA's Math Horizons ("Thee Cards Suffice" by Colm Mulcahy, Vol 22, No 2, pages 22–25, Nov 2014)

        MAA's Math Horizons ("Undiluted Hocus-Pocus" review and "The Top 10 Things Every Mathematics Student Should Know about Martin Gardner" by Colm Mulcahy, Vol 22, No 1, pages 24–25, Sep 2014)

        "Let the Games Continue" (Sci Am, co-authored with Dana Richards)

        "Math Games of Martin Gardner Still Spur Innovation" (Sci Am)

        "How Well Do You Know Martin Gardner?" (Sci Am)

        "You Don't Have to Be a Genius to Work at Subway..." (Huffington Post)

        NCTM Mathematics Teacher (pages 194-199, with Al Goetz)

        UCD Connections 2014–2015 (page 73)

        Numbers Game

        A Month of Math, Magic and Mystery (Sci Am)

        Google preview of book


        75 second TV clip


36 mins MAA Google Connected Classroom Hangout on Mathematical Magic with Cards, Apr 2014
(re: Mathematics Awareness Month, Day 3)

6 mins video by Chris Morgan of Ice Cream Trick, Oct 2013
(from Celebration of Mind resources)


A Month of Math, Magic and Mystery (Scientific American)
16 Apr 2014

Math’s Best Friend, Martin Gardner (Scientific American)
29 Oct 2013

The Magic of Math (American Univ)
25 Oct 2013

Martin Gardner–The Best Friend Mathematics Ever Had (Huff Post)
20 Oct 2013

All Squared, Number 8 (Aperiodical)
6 Oct 2013

All Squared, Number 7 (Aperiodical)
29 Sep 2013

Inspired by Math (Wild About Math)
21 Sep 2013

Let the Mathemagic Begin (Math Tango)
15 Sep 2013

Spelman’s Own ‘Mathemagician’ (Inside Spelman)
5 Sep 2013


Mathematical Card Magic: Fifty-Two New Effects, foreword by Max Maven
(AK Peters/CRC Press, 380 pages, 128 illustrations, Aug 2013)

cover art of 'Mathematical Card Magic, fifty two new effects'

"Filled with many original ideas that will keep mathematicians and magicians busy for a very long time" — Arthur Benjamin

"A lot of fun. It's clever, instructive, and clear. Learn some tricks. Learn some math. Impress your friends." — John Allen Paulos

"A stimulating collection of novel card magic tricks that .... form a wonderful introduction to important ideas in combinatorics" — Ronald Graham

"A must for your magic library" — Lennart Green


With the late Martin Gardner, in Oklahoma, Mar 2007. The famed writer was a sweet, unassuming and generous man. He played a significant role in enriching the intellectual climate of a nation during the space race era, turning tens of thousands of people on to the joys of creative thinking. In a sense, he did for mathematics what Julia Child did for French cooking. His legacy is celebrated every Oct with Celebration of Mind parties worldwide.


With Ethan Brown, in NYC, Aug 2013, at the first MOVES conference at the groundbreaking Museum of Math. Though he's only starting 9th grade, Ethan is already an energetic blogger, and a protégé of Art Benjamin. He's a total whiz at magic square completion and can do amazing mental arithmetic feats.


With Ron Graham and Persi Diaconis, in San Diego, Jan 2013, at a book signing for their beautiful and inspirational Magical Mathematics: The Mathematical Ideas that Animate Great Magic Tricks (Princeton University Press, 2011) deservedly won the 2013 Euler Book Prize. The wonderful mathematics and magic in that tome is much more sophisticated than that found in Mathematical Card Magic: Fifty-Two New Effects.

(All photos on this and related webpages are copyrighted and may not be used without permission.)
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3-7-2021 bhí an chuma air go stadfadh sé i lár abairte Níor chuala mé tagairt ar bith don chúrsa a bheith críochnaitheo Tá foirmeacha meastóireachta do chúrsa coitianta, nach ea?