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 A145856 Least number k>1 such that centered n-gonal number n*k(k-1)/2+1 is a perfect square, or 0 if there no such k exists. 0
 3, 0, 2, 4, 3, 8, 16, 2, 17, 9, 15, 5, 6, 16, 2, 3, 6, 0, 7, 4, 3, 40, 7, 2, 22, 8, 111, 4, 16, 8, 16, 0, 3, 9, 2, 5, 990, 9, 15, 3, 46, 16, 10, 5, 6, 336, 10, 2, 30, 0, 31, 16, 11, 416, 7, 3, 11, 33, 55, 4, 78, 56, 2, 6, 3, 8, 47751, 12, 16, 24, 48, 0, 49, 25, 17, 13, 6, 9, 2640, 2, 6721 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES Jonathan Vos Post, When Centered Polygonal Numbers are Perfect Squares, submitted to Mathematics Magazine, 4 May 2004, manuscript no. 04-1165, unpublished, available upon request [From Jonathan Vos Post, Oct 25 2008] LINKS E. Weisstein, MathWorld, Centered Polygonal Numbers FORMULA a(n) = 0 for n in A166259. a(n) = A120744(n) + 1. [From Alexander Adamchuk, Oct 10 2009] CROSSREFS Cf. A120744, A001542, A166259, A006451, A001921, A129444, A001570, A001652, A129556, A053606, A105038, A105040, A053141, A061278. Sequence in context: A190013 A171088 A058624 * A092154 A177344 A139585 Adjacent sequences:  A145853 A145854 A145855 * A145857 A145858 A145859 KEYWORD nonn AUTHOR Alexander Adamchuk, Oct 22 2008 EXTENSIONS Edited by Max Alekseyev, Jan 20 2010 Edited by Max Alekseyev, Jan 23 2010 STATUS approved

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Last modified September 24 15:33 EDT 2021. Contains 347643 sequences. (Running on oeis4.)