tetrahedral number

English

Noun

tetrahedral number (plural tetrahedral numbers)

(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 ${(n+1)^{3}-(n+1) \over 6}$ .

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