A011902 [ n(n-1)(n-2)/20 ].

0, 0, 0, 0, 1, 3, 6, 10, 16, 25, 36, 49, 66, 85, 109, 136, 168, 204, 244, 290, 342, 399, 462, 531, 607, 690, 780, 877, 982, 1096, 1218, 1348, 1488, 1636, 1795, 1963, 2142, 2331, 2530, 2741, 2964, 3198, 3444

Offset

0,6

Links

Table of n, a(n) for n=0..42.

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

Formula

a(n) = +3*a(n-1) -3*a(n-2) +a(n-3) +a(n-20) -3*a(n-21) +3*a(n-22) -a(n-23). G.f.: x^4*(1+x^4+x^5-x^6+2*x^8-2*x^9+3*x^10-2*x^11+2*x^12-x^13+2*x^15-x^17+x^18) / ( (-1+x)^4*(1+x^4+x^3+x^2+x)*(1+x)*(1-x+x^2-x^3+x^4)*(1+x^2)*(x^8-x^6+x^4-x^2+1) ). [From R. J. Mathar, Apr 15 2010]

Mathematica

Table[Floor[(n(n-1)(n-2))/20], {n, 0, 80}]  (* Harvey P. Dale, Mar 23 2011 *)

Crossrefs

Sequence in context: A173691 A280709 A025222 * A025004 A145131 A265072

Adjacent sequences: A011899 A011900 A011901 * A011903 A011904 A011905

Keyword

nonn

Author

N. J. A. Sloane.

Status

approved