A011892 - OEIS

A011892

a(n) = floor( n*(n-1)*(n-2)/10 ).

0, 0, 0, 0, 2, 6, 12, 21, 33, 50, 72, 99, 132, 171, 218, 273, 336, 408, 489, 581, 684, 798, 924, 1062, 1214, 1380, 1560, 1755, 1965, 2192, 2436, 2697, 2976, 3273, 3590, 3927, 4284, 4662, 5061, 5483, 5928, 6396, 6888, 7404, 7946, 8514, 9108, 9729, 10377, 11054, 11760

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OFFSET

0,5

LINKS

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

Index entries for linear recurrences with constant coefficients, signature (3,-3,1,0,1,-3,3,-1).

FORMULA

From R. J. Mathar, Apr 15 2010: (Start)

a(n) = +3*a(n-1) -3*a(n-2) +a(n-3) +a(n-5) -3*a(n-6) +3*a(n-7) -a(n-8).

G.f.: x^4*(2+x^3)/( (1-x)^4*(1+x+x^2+x^3+x^4) ). (End)

MATHEMATICA

CoefficientList[Series[x^4*(2+x^3)/((1-x)^3*(1-x^5)), {x, 0, 50}], x] (* Vincenzo Librandi, Jul 07 2012 *)