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 A277087 #50 Dec 16 2016 14:17:53
%S A277087 1,2,10,14,10,22,910,2,170,266,110,46,910,2,290,4774,170,2,639730,2,
%T A277087 4510,602,230,94,15470,22,530,266,290,118,18928910,2,170,21574,10,
%U A277087 1562,46700290,2,10,1106,76670,166,1134770,2,20470,90706,470,2,1500590,2,11110,1442,530,214,69730570,506,557090,14,590,2,776085310
%N A277087 a(0) = 1, a(n) = (denominator of the Bernoulli number B_{2n})/3, for n>=1.
%C A277087 All terms except a(0) are odd multiples of 2, by the von Staudt-Clausen theorem. See A002445 and A027642 for comments, references, and links.
%H A277087 Robert Israel, <a href="/A277087/b277087.txt">Table of n, a(n) for n = 0..10000</a>
%F A277087 a(0) = 1, a(n) = (1/3)*A002445(n) = (1/3)*A027642(2*n) = (2/3)*A001897(n) for n>0.
%p A277087 1, seq(denom(bernoulli(2*n))/3,n=1..100); # _Robert Israel_, Dec 16 2016
%t A277087 Join[{1}, Denominator[BernoulliB[Range[2, 120, 2]]]/3]
%o A277087 (PARI) a(n)=ceil(denominator(bernfrac(2*n))/3) \\ _Charles R Greathouse IV_, Dec 16 2016
%Y A277087 Cf. A001897, A002445, A027642.
%K A277087 nonn,frac
%O A277087 0,2
%A A277087 _Jonathan Sondow_, Dec 12 2016