A212772 - OEIS

A212772

a(n) = floor((n+1)*(n-3)*(n-4)/12).

1, 1, 0, 0, 0, 1, 3, 8, 15, 25, 38, 56, 78, 105, 137, 176, 221, 273, 332, 400, 476, 561, 655, 760, 875, 1001, 1138, 1288, 1450, 1625, 1813, 2016, 2233, 2465, 2712, 2976, 3256, 3553, 3867, 4200, 4551, 4921, 5310, 5720, 6150, 6601, 7073, 7568, 8085, 8625, 9188, 9776, 10388, 11025, 11687, 12376, 13091, 13833, 14602, 15400, 16226

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OFFSET

0,7

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Dominique Bénard, Orientable imbedding of line graphs, J. Combinatorial Theory Ser. B 24 (1978), no. 1, 34--43. MR0485482(58 #5312)

Index entries for linear recurrences with constant coefficients, signature (3,-3,1,1,-3,3,-1).

FORMULA

G.f.: (1-2*x+2*x^3-2*x^4+3*x^5)/((1+x+x^2+x^3)*(1-x)^4). [Bruno Berselli, May 26 2012]

a(n) = 1+(2*(n-5)*(n-1)*n-3*(1+(-1)^n)*(1-i^((n-1)*n)))/24, where i=sqrt(-1). [Bruno Berselli, May 26 2012]

MATHEMATICA

Table[Floor[(n + 1) (n - 3) ((n - 4)/12)], {n, 0, 60}] (* Bruno Berselli, May 26 2012 *)

PROG

(Magma) m:=61; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((1-2*x+2*x^3-2*x^4+3*x^5)/((1+x+x^2+x^3)*(1-x)^4))); // Bruno Berselli, May 26 2012

(Maxima) makelist(1+(2*(n-5)*(n-1)*n-3*(1+(-1)^n)*(1-%i^((n-1)*n)))/24, n, 0, 60); [Bruno Berselli, May 26 2012]

CROSSREFS

Sequence in context: A274696 A367064 A022451 * A238806 A080181 A071399

Adjacent sequences: A212769 A212770 A212771 * A212773 A212774 A212775

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, May 26 2012

STATUS

approved