G.H. Hardy once visited Ramanujan in the hospital and mentioned he'd arrived in a taxi numbered 1729, calling it a rather dull number. Ramanujan immediately replied that it wasn't dull at all: 1729 is the smallest number expressible as the sum of two cubes in two different ways. It's now called the Hardy-Ramanujan number, and "taxicab numbers" are named after this story.

The two decompositions:

 1^3 + 12^3  =     1 + 1728  =  1729
 9^3 + 10^3  =   729 + 1000  =  1729