Its claim to fame
and (unless you count ) this is the only square number that is a sum of squares of consecutive numbers starting at 1. This means that if you make a square pyramid by piling up cannonballs the only possible number of cannonballs is 4,900.
Proving 4900 is the only solution is not at all easy. The first attempts were in the late 19th century and different proofs were published over a span of more that 100 years. See https://en.wikipedia.org/wiki/Cannonball_problem