The Two Envelopes Problem
One envelope holds twice as much money as the other. The arithmetic says swap — then says swap back, forever.
1953 (Littlewood, crediting Schrödinger), 1989 (envelope form)19 min read
Belgian recreational mathematics and number theory
Maurice Kraitchik
1882 – 1957
Number theorist who worked on factorisation methods that later fed into the quadratic sieve, and an editor of the journal Sphinx. He is remembered here for his recreational writing: the necktie paradox and the wallet game in his "Mathematical Recreations" are the earliest widely circulated forms of what is now the two envelopes problem. He posed the puzzle without resolving it.