%I #5 Mar 30 2012 18:38:52
%S 1,18,1944,524880,264539520,214277011200,254561089305600,
%T 416971064282572800,900657498850357248000,2480410751833883860992000,
%U 8483004771271882804592640000,35272333838948488701496197120000
%N a(n)=-1/b(2n) where 1/(e^y-e^(y/3))= sum(i=-1,inf,b(i)*y^i).
%F a(n)=A007661(6n+1)=A032031(3n+1)
%K easy,nonn
%O 0,2
%A _Benoit Cloitre_, Mar 12 2002