Pyramidal Number
A Figurate Number corresponding to a configuration of points which form a pyramid with 
-sided RegularPolygon bases can be thought of as a generalized pyramidal number, and has the form
 | (1) |
 |  |  | (2) |
 | |  | (3) |
 | |  | (4) |
so
corresponds to a Tetrahedral Number 
, and 
to a Square Pyramidal Number 
.The pyramidal numbers can also be generalized to 4-D and higher dimensions (Sloane and Plouffe 1995).
See also Heptagonal Pyramidal Number, Hexagonal Pyramidal Number, Pentagonal Pyramidal Number, SquarePyramidal Number, Tetrahedral Number
References
Conway, J. H. and Guy, R. K. ``Tetrahedral Numbers'' and ``Square Pyramidal Numbers'' The Book of Numbers. New York: Springer-Verlag, pp. 44-49, 1996. Sloane, N. J. A. and Plouffe, S. ``Pyramidal Numbers.'' Extended entry for sequence M3382 in The Encyclopedia of Integer Sequences. San Diego, CA: Academic Press, 1995.
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