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 A069174 Centered 23-gonal numbers. 4
 1, 24, 70, 139, 231, 346, 484, 645, 829, 1036, 1266, 1519, 1795, 2094, 2416, 2761, 3129, 3520, 3934, 4371, 4831, 5314, 5820, 6349, 6901, 7476, 8074, 8695, 9339, 10006 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Ivan Panchenko, Table of n, a(n) for n = 1..1000 E. Weisstein, Centered Polygonal Numbers Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = (23*n^2 - 23*n + 2)/2. a(n) = 23*n+a(n-1)-23 (with a(1)=1). - Vincenzo Librandi, Aug 08 2010 From Amiram Eldar, Jun 21 2020: (Start) Sum_{n>=1} 1/a(n) = 2*Pi*tan(sqrt(15/23)*Pi/2)/sqrt(345). Sum_{n>=1} a(n)/n! = 25*e/2 - 1. Sum_{n>=1} (-1)^n * a(n)/n! = 25/(2*e) - 1. (End) MATHEMATICA FoldList[#1 + #2 &, 1, 23 Range@ 45] (* Robert G. Wilson v, Feb 02 2011 *) PROG (PARI) a(n)=(23*n^2-23*n+2)/2 \\ Charles R Greathouse IV, Jun 17 2017 CROSSREFS Cf. centered polygonal numbers listed in A069190. Sequence in context: A319972 A304157 A051876 * A124717 A126378 A320702 Adjacent sequences:  A069171 A069172 A069173 * A069175 A069176 A069177 KEYWORD nonn,easy AUTHOR Terrel Trotter, Jr., Apr 09 2002 STATUS approved

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Last modified August 7 15:30 EDT 2020. Contains 336276 sequences. (Running on oeis4.)