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A028991 Odd 9-gonal (or enneagonal) numbers. 1
1, 9, 75, 111, 261, 325, 559, 651, 969, 1089, 1491, 1639, 2125, 2301, 2871, 3075, 3729, 3961, 4699, 4959, 5781, 6069, 6975, 7291, 8281, 8625, 9699, 10071, 11229, 11629, 12871, 13299, 14625, 15081, 16491, 16975, 18469, 18981, 20559, 21099 (list; graph; refs; listen; history; internal format)
OFFSET

0,2

LINKS

Eric Weisstein's World of Mathematics, Source

FORMULA

(1/2)[28n^2 + 4n + 1 + (14n+1)(-1)^n].

CROSSREFS

Cf. A001106, A028992.

Sequence in context: A178827 A190984 A001716 * A102094 A125397 A095249

Adjacent sequences:  A028988 A028989 A028990 * A028992 A028993 A028994

KEYWORD

nonn

AUTHOR

Patrick De Geest (pdg(AT)worldofnumbers.com)

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Last modified February 16 21:51 EST 2012. Contains 205978 sequences.