There are N triangles in a N-gon
There are 15 triangles in a 17-agon
There are 48 triangles in a 50-gon polygon
There are: 13-2 = 11 triangles
There are: 23-2 = 21 triangles
There are 67-2 = 65 triangles
n - 2 triangles
There are 20
N
14
There are 11
1000