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A124135 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. 0

%I

%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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Last modified October 16 14:09 EDT 2021. Contains 348042 sequences. (Running on oeis4.)