Definition:Hexagonal Pyramidal Number

Definition
Hexagonal pyramidal numbers are those denumerating a collection of objects which can be arranged in the form of a hexagonal pyramid.

The $n$th hexagonal pyramidal number $P_n$ is defined as:
 * $\displaystyle P_n = \sum_{k \mathop = 1}^n H_k$

where $H_k$ is the $k$th hexagonal number.

Also known as
Hexagonal pyramidal numbers are also known as greengrocers' numbers.

Also see

 * Definition:Pyramidal Number
 * Definition:Tetrahedral Number
 * Definition:Square Pyramidal Number
 * Definition:Pentagonal Pyramidal Number