How many triangles form by the diagonals from a fixed vertex has 11 12 13 14 15 sided polygon

If we draw diagonals from a fixed vertex of a n sided polygon, there will be (n-2) number of triangles formed.

So for n=11, number of triangles formed = 9

for n=12, number of triangles formed = 10

for n=13, number of triangles formed = 11

for n=14, number of triangles formed = 12

for n=15, number of triangles formed = 13