Heptagonal /(?)/

Hep·tag·o·nal

Heptagonal

a.
  1. Having seven angles or sides.

Phrases & Compounds
Heptagonal numbers
the numbers of the series 1, 7, 18, 34, 55, etc., being figurate numbers formed by adding successively the terms of the arithmetical series 1, 6, 11, 16, 21, etc.