tetrahedral number

English

Noun

tetrahedral number (plural tetrahedral numbers)

1. (mathematics) A number which results from the summation of consecutive triangular numbers, starting from 1. If the triangular numbers in such a summation are depicted as horizontal triangular arrays of units then these arrays can be stacked vertically to yield a tetrahedral array.

   The $n$^th tetrahedral number can be calculated with the formula ${(n+1)^{3}-(n+1) \over 6}$.