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 A195046 Concentric 15-gonal numbers. 6
 0, 1, 15, 31, 60, 91, 135, 181, 240, 301, 375, 451, 540, 631, 735, 841, 960, 1081, 1215, 1351, 1500, 1651, 1815, 1981, 2160, 2341, 2535, 2731, 2940, 3151, 3375, 3601, 3840, 4081, 4335, 4591, 4860, 5131, 5415, 5701, 6000, 6301, 6615, 6931, 7260, 7591 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (2, 0, -2, 1). FORMULA a(n) = 15*n^2/4+11*((-1)^n-1)/8. a(0)=0, a(1)=1, a(2)=15, a(3)=31, a(n)=2*a(n-1)-2*a(n-3)+a(n-4) [From Harvey P. Dale, Feb 23 2012] G.f.: -((x*(1+x*(13+x)))/((-1+x)^3*(1+x))) [From Harvey P. Dale, Feb 23 2012] MATHEMATICA Table[15n^2/4+11((-1)^n-1)/8, {n, 0, 50}] (* or *) LinearRecurrence[ {2, 0, -2, 1}, {0, 1, 15, 31}, 50] (* Harvey P. Dale, Feb 23 2012 *) PROG (PARI) a(n)=15*n^2/4+11*((-1)^n-1)/8 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Column 15 of A195040. Cf. A032527, A032528, A195045, A195047, A195145, A195146. Sequence in context: A132757 A045135 A283122 * A102955 A041444 A041446 Adjacent sequences:  A195043 A195044 A195045 * A195047 A195048 A195049 KEYWORD nonn,easy AUTHOR Omar E. Pol, Sep 27 2011 EXTENSIONS Corrected (a(1)=1 added) by Harvey P. Dale, Feb 23 2012 STATUS approved

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