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 A014633 Even pentagonal numbers. 5
 0, 12, 22, 70, 92, 176, 210, 330, 376, 532, 590, 782, 852, 1080, 1162, 1426, 1520, 1820, 1926, 2262, 2380, 2752, 2882, 3290, 3432, 3876, 4030, 4510, 4676, 5192, 5370, 5922, 6112, 6700, 6902, 7526, 7740, 8400, 8626, 9322 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..10000 Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1). FORMULA G.f.: 2*(6+5*x+12*x^2+x^3)/((1+x)^2*(1-x)^3). - Maksym Voznyy (voznyy(AT)mail.ru), Aug 11 2009, corrected by R. J. Mathar, Sep 16 2009 From Ant King, Aug 16 2011: (Start) a(n) = a(n-1) +2*a(n-2) -2*a(n-3) -a(n-4) +a(n-5). a(n) = 48+2*a(n-2)-a(n-4). a(n) = 1/8*(1-3*(-1)^(n+1)+12*(n+1))*(1-(-1)^(n+1)+4*(n+1)).(End) MATHEMATICA LinearRecurrence[{1, 2, -2, -1, 1}, {0, 12, 22, 70, 92}, 40] (* Harvey P. Dale, Aug 26 2014 *) Select[PolygonalNumber[5, Range[0, 100]], EvenQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 15 2017 *) PROG (MAGMA) [1/8*(1-3*(-1)^(n+1)+12*(n+1))*(1-(-1)^(n+1)+4*(n+1)): n in [0..40]]; // Vincenzo Librandi, Aug 17 2011 (PARI) lista(nn) = {forstep (n=0, nn, 2, if (ispolygonal(n, 5), print1(n, ", ")); ); } \\ Michel Marcus, Jun 20 2015 CROSSREFS Cf. A000326. Sequence in context: A200197 A115709 A115703 * A298323 A299216 A227072 Adjacent sequences:  A014630 A014631 A014632 * A014634 A014635 A014636 KEYWORD nonn,easy AUTHOR EXTENSIONS More terms from Patrick De Geest STATUS approved

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Last modified December 5 13:26 EST 2019. Contains 329751 sequences. (Running on oeis4.)