This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A090814 #7 Apr 20 2019 08:50:27
%S A090814 11,1093,3851,797161,64570081,581130733,1001523179,581613367499,
%T A090814 308836698141973,225141952945498681,219716845645607147,
%U A090814 164128483697268538813,13294407179478751643893,90575914334953364003723
%N 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.
%C A090814 Appears to be an integer for n from 3 up to 250.
%t A090814 pB[n_]:=Module[{p=Prime[n]},3 (3^p-1)/Denominator[BernoulliB[2p]]]; Array[ pB,20,3] (* _Harvey P. Dale_, Apr 20 2019 *)
%o A090814 (PARI) a(n)=3*(3^prime(n)-1)/denominator(bernfrac(2*prime(n)))
%K A090814 nonn
%O A090814 3,1
%A A090814 _Benoit Cloitre_, Feb 11 2004