Why 1729?

1729 is well known in maths circles as the ‘taxicab’ number or the 'Hardy–Ramanujan' number, which came from a conversation over a hundred years ago involving mathematicians G. H. Hardy and Srinivasa Ramanujan.

As later told by Hardy: “I remember once going to see him [Ramanujan] when he was lying ill at Putney. I had ridden in taxi-cab number 1729 and remarked that the number seemed to be rather a dull one, and that I hoped it was not an unfavourable omen. ‘No,’ he replied, ‘it is a very interesting number; it is the smallest number expressible as the sum of two cubes in two different ways.’”

The number 1729 is also a wonderful number in maths. For example, it is a Harshad number in base 10 and it’s also the first Carmichael number. And for anyone wondering if the year is also significant; it was the year Newton’s Principia was first published in English.