icosihenagon

An icosihenagon is a polygon with 21 sides and 21 vertices. The word "icosihenagon" comes from the Greek words "eikosi" meaning twenty and "gonia" meaning angle. In geometry, a polygon is a closed shape made up of straight line segments. The number of sides determines the specific name of the polygon.

Like all polygons, an icosihenagon has interior angles and exterior angles. The sum of the interior angles of any 21-sided polygon can be calculated using the formula (n-2) * 180 degrees, where n is the number of sides. For an icosihenagon, this would be (21-2) * 180 = 19 * 180 = 3420 degrees. If the icosihenagon is regular, meaning all sides and all angles are equal, then each interior angle measures 3420 / 21 = approximately 162.86 degrees.

A regular icosihenagon can be constructed using a compass and straightedge, although it is not a constructible polygon in the same way as, for example, a pentagon or a hexagon, which have a number of sides that are powers of two times distinct Fermat primes. The construction of a 21-gon is possible because 21 is the product of two distinct Fermat primes (3 and 7).

The term icosihenagon is not as commonly used as names for polygons with fewer sides, such as triangle, square, or pentagon. However, it follows the standard naming conventions for polygons based on their number of sides.