IMO Shortlist 1966 problem 11
Dodao/la:
arhiva2. travnja 2012. Does there exist an integer

that can be written in two different ways as

, where

are natural numbers with

?
%V0
Does there exist an integer $z$ that can be written in two different ways as $z = x! + y!$, where $x, y$ are natural numbers with $x \le y$ ?
Izvor: Međunarodna matematička olimpijada, shortlist 1966