1729 is called Ramanujan number because it is the smallest number that can be expressed as the sum of two cubes in two different ways.
What is ramanujan number?
Ramanujan number is a mathematical constant that is very difficult to calculate. It is named after the Indian mathematician Srinivasa Ramanujan.
Conclusion
1729 is called Ramanujan number because it is the smallest number expressible as the sum of two cubes in two different ways.
