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   A131118 a(4n) = -n^2, a(4n+1) = n^2, a(4n+2) = 1-n^2, a(4n+3) = n*(n+1). 2
   0, 0, 1, 0, -1, 1, 0, 2, -4, 4, -3, 6, -9, 9, -8, 12, -16, 16, -15, 20, -25, 25, -24, 30, -36, 36, -35, 42, -49, 49, -48, 56, -64, 64, -63, 72, -81, 81, -80, 90, -100, 100, -99, 110, -121, 121, -120, 132, -144, 144, -143, 156, -169, 169, -168 (list; graph; refs; listen; history; text; internal format)
   OFFSET 0,8 COMMENTS Up to signs, the first differences are in A131804. - R. J. Mathar, Mar 17 2009 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 FORMULA From R. J. Mathar, Mar 17 2009: (Start) a(n) = -2*a(n-1) -2*a(n-2) -2*a(n-3) +2*a(n-5) +2*a(n-6) +2*a(n-7) +a(n-8). G.f.: x^2*(1+x^2+x^3+2*x)/((1-x)*(1+x^2)^2*(1+x)^3). (End) a(n) = ((-2*n^2+4*n+7)*(-1)^n - 2*((n+4)+(n+2)*(-1)^n)*i^(n*(n+1))+5)/32, where i=sqrt(-1). - Bruno Berselli, Mar 27 2012 MAPLE seq(((7+4*n-2*n^2)*(-1)^n -2*((n+4)+(n+2)*(-1)^n)*(-1)^binomial(n+1, 2) +5)/32, n=0..60); # G. C. Greubel, Nov 18 2019 MATHEMATICA Table[((7+4*n-2*n^2)*(-1)^n -2*((n+4)+(n+2)*(-1)^n)*(-1)^Binomial[n+1, 2] +5)/32, {n, 0, 60}] (* G. C. Greubel, Nov 18 2019 *) PROG (PARI) a(n) = ((7+4*n-2*n^2)*(-1)^n -2*((n+4)+(n+2)*(-1)^n)*(-1)^binomial(n+1, 2) +5)/32; \\ G. C. Greubel, Nov 18 2019 (Magma) [((7+4*n-2*n^2)*(-1)^n -2*((n+4)+(n+2)*(-1)^n)*(-1)^Binomial(n+1, 2) +5)/32: n in [0..60]]; // G. C. Greubel, Nov 18 2019 (Sage) [((7+4*n-2*n^2)*(-1)^n -2*((n+4)+(n+2)*(-1)^n)*(-1)^binomial(n+1, 2) +5)/32 for n in (0..60)] # G. C. Greubel, Nov 18 2019 (GAP) List([0..60], n-> ((7+4*n-2*n^2)*(-1)^n -2*((n+4)+(n+2)*(-1)^n)*(-1)^Binomial(n+1, 2) +5)/32 ); # G. C. Greubel, Nov 18 2019 CROSSREFS Sequence in context: A135359 A098217 A151846 * A140765 A097541 A151819 Adjacent sequences: A131115 A131116 A131117 * A131119 A131120 A131121 KEYWORD sign,easy AUTHOR Paul Curtz, Sep 24 2007 EXTENSIONS More terms from Sean A. Irvine, Mar 13 2011 STATUS approved
  
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  Last modified February 23 02:31 EST 2024. Contains 370265 sequences. (Running on oeis4.)