The number 1729. In 1919, Hardy visited an ill Ramanujan and commented that his taxicab number, 1729, was rather dull. Ramanujan contradicted Hardy, saying it was, in fact, the smallest number that could be written as the sum of two cubes in two different ways, namely 1729 = 9³ + 10³ = 1³ + 12³. The term also relates to the smallest numbers which can be written in n different ways as the sum of two cubes, which Hardy and Wright later showed to exist.