cannonball problem

English

Etymology

It can be visualized as the problem of taking a square arrangement of cannonballs on the ground and building a square pyramid out of them.

Proper noun

cannonball problem

1. (mathematics) The challenge of proving that the only solution of the Diophantine equation :$\sum _{n=1}^{N}n^{2}=M^{2}\;$ with N > 1 is when N = 24 and M = 70.