Pyramidal number
A pyramidal number is a figurate number that represents a pyramid with a polygonal base and a given number of triangular sides. A pyramidal number is the number of points in a pyramid where each layer of the pyramid is an -sided polygon of points. The term usually refers to square pyramidal numbers, which have a square base with four sides, but it can also refer to pyramids with three or more sides. It is possible to extend the pyramidal numbers to higher dimensions.Formula
The formula for the th -gonal pyramidal number is
where,.
This formula can be factored:
where is the th triangular number.
