The smallest nontrivial taxicab number, i.e., the smallest number representable in two ways as a sum of two cubes. It is given by 1729 = 1^3 + 12^3 = 9^3 + 10^3.

Diophantine equation--3rd powers | taxicab number

Godfrey Harold Hardy | Srinivasa Aiyangar Ramanujan