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 A090814 a(n)=3*(3^prime(n)-1)/denominator(B(2*prime(n))) where prime(n)=n-th prime and B(k) denotes the k-th Bernoulli number. 1

%I

%S 11,1093,3851,797161,64570081,581130733,1001523179,581613367499,

%T 308836698141973,225141952945498681,219716845645607147,

%U 164128483697268538813,13294407179478751643893,90575914334953364003723

%N a(n)=3*(3^prime(n)-1)/denominator(B(2*prime(n))) where prime(n)=n-th prime and B(k) denotes the k-th Bernoulli number.

%C Appears to be an integer for n from 3 up to 250.

%t pB[n_]:=Module[{p=Prime[n]},3 (3^p-1)/Denominator[BernoulliB[2p]]]; Array[ pB,20,3] (* _Harvey P. Dale_, Apr 20 2019 *)

%o (PARI) a(n)=3*(3^prime(n)-1)/denominator(bernfrac(2*prime(n)))

%K nonn

%O 3,1

%A _Benoit Cloitre_, Feb 11 2004

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Last modified December 8 14:41 EST 2021. Contains 349596 sequences. (Running on oeis4.)