»  Brainteasers from my diaries




My diaries often close with a "Math Corner," usually set up as a brainteaser. I haven't aimed for anything heavy with these puzzles, just something for a person to while away ten minutes with during a coffee break.

Some of the puzzle solutions got a web page of their own with my solution. If a puzzle didn't get a page of its own, that was because either (a) I thought it was too easy to be worth putting up a page for, or (b) I forgot. For cases covered by (a), there would be be an appropriate note in the following month's diary. For the (b) cases, I am sorry.

[Added September 2014 : I shall very occasionally include a brainteaser in a column at some other outlet. If it justifies a worked solution, I'll post it here.]

Date Puzzle
May 2024 A fact about factorials.
April 2024 A fact about factors.
February 2024 Rock-breaking and an insight.
December 2023 Cutting up an equilateral triangle.
November 2023 The remainders have it.
October 2023 A surprising inequality.
September 2023 Messing with matchsticks.
August 2023 An easy one from Twitter … sorry: from X.
July 2023 Subtracting Around the Corner
May 2023 Flipping light switches
March 2023 A difficult inequality
February 2023 Area of a semicircle
December 2022 Harshad Numbers, Eldar Numbers, and the power [sic] of exponentiation
November 2022 From the gāokăo
October 2022 Vukmirovic sequences
September 2022 An easy one
August 2022 An extraordinary theorem
July 2022 Zimbalist numbers
June 2022 A little light wordplay
May 2022 The icing on the cake
April 2022 An interesting billionth power
March 2022 A two-variable inequality over the positive integers
February 2022 Topical solution to a sequence problem
December 2021 Spaghetti loops
October 2021 Wordplay challenge
September 2021 The first odd number in the dictionary
July 2021 IMO 2021, Problem 1
June 2021 Bailey's Triangle
May 2021 Two semicircles in a circle
April 2021 From false to true with one line
March 2021 The Stump Divisibility Theorem
February 2021 The Parker Square-Sum Problem
January 2021 The Vukmirovic Sequence
December 2020 The poorly-designed clock
November 2020 Balls in a box
October 2020 A point distant 3, 4, and 5 from the vertices of an equilateral Δ
September 2020 One from the Putnam competition
July 2020 Factorizing a super-factorial
June 2020 Gombaud's goof
May 2020 Two equilateral triangles
April 2020 Handshakes at a party
December 2019 Balls'n'boxes
November 2019 The rotating door
October 2018 Joe Shipman's casino game
August 2018 Two arithmetic sequences
May 2018 Three lighthouses
March 2018 Waiting on line
November 2017 Mystery sequence
October 2017 Two cones from a circular disk
July 2017 One of Ramanujan's
February 2017 The soft-sphere problem
December 2016 Pennies, nickels, and dimes
September 2016 The taxicab number
August 2016 Rolling three dice
January 2016 Knight covers knight: primzahlfrei months in the far future
November 2015 Expressing n as a difference of two squares
September 2014 at VDARE.com My new kitchen table
December 2011 Two random points in a disc
September 2011 Working for Solyndra
June 2011 Stroking the keys
May 2011 The Golden String
March 2011 9.94962308959395941218332 …
January 2011 The pseudorhombicuboctahedron
December 2010 The number 2011
November 2010 Multiple choice
October 2010 Burmese days …
        and hours, and years
September 2010 Derbhenge
August 2010 Derangement
June 2010 Tuesday's Child
May 2010 A Sniper's Feat
February 2010 Ackerman's Numbers
January 2010 Sequence in a Sequence
December 2009 How Many (abc)?
October 2009 Sex Ratios in an Odd Tribe
August 2009 Trying Combinations
July 2009 Add-Multiply Patterns
10-Digit Numbers
June 2009 House Numbers
May 2009 Three Blank Dice
April 2009 Three Circles
March 2009 Selecting & Omitting
January 2009 The Card Game "War"
December 2008 Facts About 2009
November 2008 Polynomial Minimaxes
Rating Sports Teams
September 2008 Inverted Numbers Difference
August 2008 Coin-Flipping Game
July 2008 Calendar Blocks
Dotted Foreheads
Broken Stick
July 2007 The Tetrahedral Torus
October 2006 What Coins Has She Got?
August 2006 Projecting France
January 2006 Man on Ball on Pole
December 2005 Pairwise Products
September 2005 Boris's Babushkas
August 2005 Chicken Nuggets
June 2005 Median Bowling Scores
May 2005 Dimensions of a Triangle
September 2004 Left-most Digits of 2N
August 2004 Nested Polygons
March 2004 X Years Old in the Year X 2
February 2004 Rossini's Birthdays
December 2003 Packaging Christmas Presents
November 2003 9M + 16N
September 2003 Schizo Brothers
July 2003 Sum & Product
June 2003 Counting Record Years
May 2003 Brothers Sell Sheep
February 2003 Dog Leashed to Lighthouse
January 2003 Her Kids' Ages
December 2002 Conversations
November 2002 Monkeys & Doors
October 2002 The Hockey Tournament
August 2002 The Monkey's Mother