Nonagonal Number

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A Figurate Number of the form , also called an Enneagonal Number. The first few are 1, 9, 24, 46, 75, 111, 154, 204, ... (Sloane's A001106).

References

Sloane, N. J. A. Sequence A001106/M4604 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.