1. Find which numbers between $1 \sim 99$ can be expressed as the sum of two squares, and which cannot.
1. $1,2,4,5,8,9,10,13,16,17,18,20,25,26,29,32,34,36,37,40,41,45,48$, $49,50,52,53,58,61,64,65,68,72,73,74,80,81,82,85,89,90,97,98$ can be expressed as the sum of two squares, while others cannot.