I started my blog about two year ago. I have written about 200 entries. According to my traffic reports, these have been the top ten most popular entries: The Odd One Out Divisibility by 7 is a Walk on a Graph, by David Wilson The Dirtiest Math...

Israel Gelfand’s memorial is being held at Rutgers on December 6, 2009. I was invited as Gelfand’s student. My relationship with Gelfand was complicated: sometimes it was very painful and sometimes it was very rewarding. I was planning to attend the...

I’ve translated two problems from the 2009 Moscow Math Olympiad. In both of them our characters are genetically engineered octopuses. The ones with an even number of arms always tell the truth; the ones with an odd number of arms always lie. In the...

An ancient Russian joke: Patient: Doctor, is there a medicine I can use to prevent my girlfriends from become pregnant? Doctor: Kefir. Patient: Should I drink it before or after sex? Doctor: Instead of. I have a more pleasurable suggestion than...

The first episode of Numb3rs: Season Six reminded me of the hangman’s paradox. Here is a one-day version of the hangman’s paradox: Suppose you are in a prison and the guard says to you, “You will be hanged tomorrow at noon and it will be a...