**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.