More about 1729.

Ofcourse any school kid can tell you that the "Ramanujan Number" 1729 is the smallest positive integer that can be written as the sum of the cubes of two numbers in two different ways.
1729 = 10^3 + 9^3 = 12^3 + 1^3
I learned few interesting stuff recently.

1+7+2+9 = 19 and 19 * 91= 1729

Consider the prime numbers 7,13 and 19 which form an arithmetic progression, 7*13*19 = 1729

1729 is not "really" the smallest number with the property that Ramanujan discovered, infact it is 91 if negative numbers are also considered.

91 = 4^3 + 3^3 = 6^3 + (-5)^3