%I #3 Mar 30 2012 18:39:24
%S 0,0,3,46,1041,32592,1375919,75858738,5309829837,460680712084,
%T 48552875077995,6111752613274230,905772678574995593,
%U 156116663818415074776,30964395850928510817831
%N a(n)=((-1)^n/6)*sum_{i1+i2+i3+i4=2n} ((2*n)!/(i1! i2! i3! i4!))*B(i1+i2+i3) where B are the Bernoulli numbers.
%F a(n)=(-1)^(n+1)*{ (9^n/4-4^n+3/4)*B(2n)+1/6}
%o (PARI) a(n)=(-1)^(n+1)*((9^n/4-4^n+3/4)*bernfrac(2*n)+1/6)
%K nonn
%O 1,3
%A _Benoit Cloitre_, Nov 30 2006
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