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a(0)=1 if n>0 a(n)=(-1)^(n+1)/(2n+1)*sum(k=0,n,4^(7k)*B(2k)*C(2n+1,2k)) where B(k) denotes the k-th Bernoulli number.
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%I #5 Mar 30 2012 18:39:10

%S 1,2731,8942387,104670662071,2400942582854087,89402734746017557411,

%T 4893960739529013452828987,369582933150490997215583309551,

%U 36809796323680462279091281973219087

%N a(0)=1 if n>0 a(n)=(-1)^(n+1)/(2n+1)*sum(k=0,n,4^(7k)*B(2k)*C(2n+1,2k)) where B(k) denotes the k-th Bernoulli number.

%o (PARI) a(n)=sum(i=0,n,4^(7*i)*bernfrac(2*i)*binomial(2*n+1,2*i))

%K nonn

%O 0,2

%A _Benoit Cloitre_, Oct 19 2002