Tetrahedral Number

A tetrahedral number, or triangular pyramidal number, is a figurate number that represents a pyramid with a triangular base and three sides, called a tetrahedron. The nth tetrahedral number is the sum of the first n triangular numbers.

The first few tetrahedral numbers are:

1, 4, 10, 20, 35, 56, 84, 120, 165, 220, 286, 364, 455, 560, 680, 816, 969, … (sequence A000292 in OEIS)

Read more about Tetrahedral Number:  Formula, Geometric Interpretation, Properties

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