Brocard’s problem

Brocard’s problem, first posed by Henri Brocard in 1876, asks for factorials that are one less than a square, that is, solutions to the equation $n!+1=m^2$. Only three solutions are known: $4!+1=5^2$, $5!+1={11}^2$ and $7!+1={71}^2$. Srinivasa Ramanujan also pondered the problem, in 1913. Erdős believed that there are no other solutions, and no more have been found for $n$ up to ${10}^9$.