Definition:Centered Hexagonal Number

Definition
A centered hexagonal number is a figurate number which is represented by:
 * a point in the center
 * all other points surrounding the center at the points of a triangular lattice.

Also known as
A centered hexagonal number can also be referred to as a hex number.

However, as this can be confused with a hexagonal number this neat and compact term is discouraged on.

Also see

 * Closed Form for Centered Hexagonal Numbers
 * Centered Hexagonal Number as Sum of Triangular Numbers