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A028992
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Even 9-gonal (or enneagonal) numbers.
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2
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0, 24, 46, 154, 204, 396, 474, 750, 856, 1216, 1350, 1794, 1956, 2484, 2674, 3286, 3504, 4200, 4446, 5226, 5500, 6364, 6666, 7614, 7944, 8976, 9334, 10450, 10836, 12036, 12450, 13734, 14176, 15544, 16014, 17466, 17964, 19500, 20026, 21646
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 0..10000
Eric Weisstein's World of Mathematics, Nonagonal Number
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FORMULA
| a(n) = (1/2)*(28*(n-1)^2 + 60*(n-1) + 33 + (14*(n-1)+15)*(-1)^(n-1)).
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PROG
| (MAGMA) [(1/2)*(28*(n-1)^2 + 60*(n-1) + 33 + (14*(n-1)+15)*(-1)^(n-1)): n in [0..40]]; // Vincenzo Librandi, Aug 19 2011
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CROSSREFS
| Cf. A001106.
Cf. A014642, A028991, A028994. - Omar E. Pol, Aug 19 2011
Sequence in context: A000496 A063323 A154590 * A040552 A199545 A098427
Adjacent sequences: A028989 A028990 A028991 * A028993 A028994 A028995
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KEYWORD
| nonn,easy
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AUTHOR
| Patrick De Geest (pdg(AT)worldofnumbers.com)
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EXTENSIONS
| 0 inserted, offset and formula corrected by Omar E. Pol, Aug 19 2011
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