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A011909 a(n) = floor( n*(n-1)*(n-2)/27 ). 0

%I

%S 0,0,0,0,0,2,4,7,12,18,26,36,48,63,80,101,124,151,181,215,253,295,342,

%T 393,449,511,577,650,728,812,902,998,1102,1212,1329,1454,1586,1726,

%U 1874,2030,2195,2368,2551,2742,2943

%N a(n) = floor( n*(n-1)*(n-2)/27 ).

%F G.f.: x^5 (1-x+x^2) (2-2 x-x^2+3 x^3-2 x^4+3 x^6-3 x^7+2 x^9-x^10-x^11+3 x^12-2 x^13-x^14+3 x^15-2 x^16+2 x^18-2 x^19+x^20)/((-1+x)^4 (1+x^3+x^6) (1+x^9+x^18)). - _Peter J. C. Moses_, Jun 02 2014

%K nonn

%O 0,6

%A _N. J. A. Sloane_.

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Last modified October 27 00:02 EDT 2021. Contains 348270 sequences. (Running on oeis4.)