# Heptagonal pyramidal number

In mathematics, a heptagonal pyramidal number is a figurate number representing the number of dots in a three-dimensional pattern in the shape of a heptagonal pyramid.[1]

The first few heptagonal pyramidal numbers are:[2]

1, 8, 26, 60, 115, 196, 308, 456, 645, 880, 1166, 1508, 1911, ... (sequence A002413 in the OEIS)

The nth heptagonal number can be calculated by adding up the first n heptagonal numbers, or more directly by using the formula[1][2]

${\displaystyle {\frac {n(n+1)(5n-2)}{6}}.}$

## References

1. ^ a b Deza, Elena; Deza, M. (2012), Figurate Numbers, World Scientific, p. 92, ISBN 9789814355483.
2. ^ a b Beiler, Albert H. (1966), Recreations in the Theory of Numbers: The Queen of Mathematics Entertains, Courier Dover Publications, p. 194, ISBN 9780486210964.