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 A140812 #10 Dec 22 2017 16:36:24
%S A140812 3,9,60,84,60,132,5460,12,1020,1596,660,276,5460,12,1740,28644,1020,
%T A140812 12,3838380,12,27060,3612,1380,564,92820,132,3180,1596,1740,708,
%U A140812 113573460,12,1020,129444,60,9372,280201740,12,60,6636,460020,996,6808620,12,122820
%N A140812 a(n) = A051717(2n) + A051717(2n+1).
%C A140812 All terms are multiples of 3.
%H A140812 G. C. Greubel, <a href="/A140812/b140812.txt">Table of n, a(n) for n = 0..2500</a>
%p A140812 C:=proc(n) if n=0 then RETURN(1); fi; if n mod 2 = 0 then RETURN(bernoulli(n)+bernoulli(n-1)); else RETURN(-bernoulli(n)-bernoulli(n-1)); fi; end:
%p A140812 A051717 := proc(n) denom(C(n)) ; end: A140812 := proc(n) A051717(2*n)+A051717(2*n+1) ; end: seq(A140812(n),n=0..80) ; # _R. J. Mathar_, Jun 28 2009
%t A140812 A051717 := Join[{1}, Denominator[Total /@ Partition[BernoulliB[Range[0, 500]], 2, 1]]]; Join[{3, 9}, Table[2*A051717[[2*n]], {n, 3,30}]] (* _G. C. Greubel_, Dec 22 2017 *)
%Y A140812 Cf. A129826, A140333.
%K A140812 nonn
%O A140812 0,1
%A A140812 _Paul Curtz_, Jul 16 2008
%E A140812 Edited and extended by _R. J. Mathar_, Jun 28 2009