Numbers

1 is the ultimate prime

2 is prime because it is inseparable from the base 10 math that 1+1, 2x1, or 2/1 all = 2

3 is the first non defacto prime. 
3 x 3 is 9

10 is the first double digit integer.
9 x 10 is 90

4 is the first non prime integer.
4 x 90 is 360

360 brings us to a circle

which proves a square.