36- is a square triangular number, i.e., it can be represented as both a square & triangle using x’s or o’s
(I tried the triangle above..try it yourself, you should get it!)
x x x x x x
x x x x x x
x x x x x x
x x x x x x
x x x x x x
x x x x x x
.
x
x x
x x x
x x x x
x x x x x
x x x x x x
x x x x x x x
x x x x x x x x
.