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 A168426 #19 Dec 21 2016 12:06:25
%S A168426 3,6,6,30,15,30,30,15,15,30,42,105,105,105,42,42,21,105,105,21,42,30,
%T A168426 105,105,105,105,105,30,30,15,105,105,105,105,15,30,66,165,165,1155,
%U A168426 231,1155,165,165,66,66,33,165,165,231,231,165,165,33,66,2730,15015,15015,15015,15015,15015,15015,15015
%N A168426 Square array of denominators of a truncated array of Bernoulli twin numbers (A168516), read by antidiagonals.
%C A168426 Entries are multiples of 3.
%C A168426 The sequence of fractions A051716()/A051717() is a sequence of first differences of A164555()/A027642().
%C A168426 It can be observed (see the difference array in A190339) that A168516/A168426 is a sequence of autosequences of the second kind. - _Paul Curtz_, Dec 21 2016
%t A168426 max = 11; c[0] = 1; c[n_?EvenQ] := BernoulliB[n] + BernoulliB[n-1]; c[n_?OddQ] := -BernoulliB[n] - BernoulliB[n-1]; cc = Table[c[n], {n, 0, max+1}]; diff = Drop[#, 2]& /@ Table[ Differences[cc, n], {n, 0, max-1}]; Flatten[ Table[ diff[[n-k+1, k]], {n, 1, max}, {k, 1, n}]] // Denominator (* _Jean-François Alcover_, Aug 09 2012 *)
%Y A168426 Cf. A085738, A085737, A168516, A190339, A240581/A239315.
%K A168426 nonn,tabl,frac
%O A168426 0,1
%A A168426 _Paul Curtz_, Nov 25 2009
%E A168426 More terms from _R. J. Mathar_, Jul 10 2011