### Instruction: What is special about the number 1729?
### Input: The number 1729 is known as the Hardy–Ramanujan number after a famous visit by Hardy to see Ramanujan at a hospital. In Hardy's words:

I remember once going to see him when he was ill at Putney. I had ridden in taxi cab number 1729 and remarked that the number seemed to me rather a dull one, and that I hoped it was not an unfavorable 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."

Immediately before this anecdote, Hardy quoted Littlewood as saying, "Every positive integer was one of [Ramanujan's] personal friends."

The two different ways are:

1729
=
1
3
+
12
3
=
9
3
+
10
3
.
{\displaystyle 1729=1^{3}+12^{3}=9^{3}+10^{3}.}
Generalisations of this idea have created the notion of "taxicab numbers".
### Response: 1729, known as the Hardy–Ramanujan number, is the smallest integer that can be expressed as the sum of the cubes of two unique pairs of integers.