diagonals divide the interior into is given by

For n-gons with n=3, 4, ... the number of regions is
:1, 4, 11, 25, 50, 91, 154, 246...

This is OEIS sequence A006522.

Intersections of diagonals

If no three diagonals of a convex polygon are concurrent at a point in the interior, the number of interior intersections of diagonals is given by . This holds, for example, for any regular polygon with an odd number of sides. The formula

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