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%I #5 Mar 30 2012 18:39:10
%S 11,115,5591,502855,73213571,15658809595,4619488631951,
%T 1797261609272335,891557677006596731,549227657514325603075,
%U 411352737726238344243911,368106640606171635113513815
%N a(n)=(-1)^(n+1)/(2n+1)*sum(k=0,n,64^k*B(2k)*C(2n+1,2k)) where B(k) denotes the k-th Bernoulli number.
%C a(2m-1) is of the form 10k+1, a(2m) is of the form 10k+5
%o (PARI) a(n)=(-1)^(n+1)/(2*n+1)*sum(k=0,n,64^k*bernfrac(2*k)*binomial(2*n+1,2*k))
%K nonn
%O 1,1
%A _Benoit Cloitre_, Oct 19 2002