Heptagonal Pyramidal Number

A Pyramidal Number of the form $n(n+1)(5n-2)/6$, The first few are 1, 8, 26, 60, 115, ... (Sloane's A002413). The Generating Function for the heptagonal pyramidal numbers is

$${x(4x+1)\over(x-1)^4}=x+8x^2+26x^3+60x^4+\ldots.$$

References

Sloane, N. J. A. Sequence A002413/M4498 in ``An On-Line Version of the Encyclopedia of Integer Sequences.'' http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S. The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.