%I A061866
%S A061866 0,0,0,1,2,4,8,13,20,30,42,57,76,98,124,155,190,230,276,327,384,448,518,
               595,680,
%T A061866 772,872,981,1098,1224,1360,1505,1660,1826,2002,2189,2388,2598,2820,3055,
%U A061866 3302,3562,3836,4123,4424,4740,5070,5415,5776,6152,6544,6953,7378,7820
%N A061866 a(n) = DivSumChoose(n,3), the number of solutions to x+y+z = 0 mod 3, 
               where 1 <= x < y < z <= n.
%C A061866 (1+x)*(1+x^2)*(1+x^3) / ( (1-x)*(1-x^2)*(1-x^3)*(1-x^4)) is the Poincare 
               series (or Molien series) for H^*(O_4(q); F_2).
%D A061866 A. Adem and R. J. Milgram, Cohomology of Finite Groups, Springer-Verlag, 
               2nd. ed., 2004; p. 233.
%F A061866 G.f.: x^3*(1+x)*(1+x^2)*(1+x^3) / ( (1-x)*(1-x^2)*(1-x^3)*(1-x^4)). - 
               N. J. A. Sloane (njas(AT)research.att.com), Mar 17 2004
%Y A061866 The third diagonal of A061865.
%Y A061866 Sequence in context: A084684 A011907 A056133 this_sequence A130840 A115266 
               A026039
%Y A061866 Adjacent sequences: A061863 A061864 A061865 this_sequence A061867 A061868 
               A061869
%K A061866 nonn
%O A061866 0,5
%A A061866 Antti Karttunen May 11 2001