icosihenagonal

An icosihenagon is a polygon with 21 sides and 21 vertices. The word "icosihenagon" is derived from the Greek words "eíkosi" meaning twenty and "hēnná" meaning one, and "gōnia" meaning corner or angle.

In a regular icosihenagon, all sides are of equal length, and all interior angles are equal. The sum of the interior angles of any icosihenagon, regardless of whether it is regular or irregular, can be calculated using the formula (n-2) * 180 degrees, where 'n' is the number of sides. For an icosihenagon, this sum is (21-2) * 180 = 19 * 180 = 3420 degrees.

The measure of each interior angle in a regular icosihenagon is 3420 degrees / 21, which is approximately 162.86 degrees. The exterior angle of a regular icosihenagon is 360 degrees / 21, approximately 17.14 degrees.

The number of diagonals in an icosihenagon can be calculated using the formula n(n-3)/2. For an icosihenagon, this is 21(21-3)/2 = 21 * 18 / 2 = 189.