A087539 - OEIS

%I #4 Mar 30 2012 18:41:20

%S 0,0,1,2,3,5,7,10,12,15,18,22,26,30,35,40,46,51,57,63,70,77,84,92,100,

%T 109,117,126,135,145,155,165,176,187,199,210,222,234,247,260,273,287,

%U 301,316,330,345,360,376,392,408,425,442,460,477,495,513

%N First differences of A011849.

%F [ C(n+1, 3)/3 ] - [ C(n, 3)/3 ].

%F G.f.: [x^3(1-x+x^2)(1-x^2+x^3)]/[(1-x)^3(1+x^3+x^6)].

%K nonn,easy

%O 1,4

%A _Ralf Stephan_, Oct 24 2003