The Greek suffix hexa- means 'six'. A hexagon is a six-sided polygon. A hexahedron is a six-sided polyhedron, otherwise known as a cube if it is regular. Hexadecimal is the number system with base 16 (i.e., six more than decimal system) and is used mostly in computing (because four binary digits can represent 16 different numbers). Hexagonal numbers are figurate numbers (numbers that can be represented by a regular geometric arrangement of equally spaced points) of the form n(2n – 1); the first few are 1, 6, 15, 28, 45, ... For hexaflexagon see flexagon. For hexomino see polyomino.