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 A172031 #6 Apr 15 2013 11:10:33
%S A172031 1,1,2,6,3,30,15,70,35,210,105,2310,1155,10010,5005,30030,15015,
%T A172031 510510,255255,3233230,1616615,1939938,969969,44618574,22309287,
%U A172031 74364290,37182145,223092870,111546435,6469693230,3234846615,66853496710,33426748355,200560490130
%N A172031 Denominator of the fraction c(n) defined in A172030.
%t A172031 c[n_] := 2*c[n-1] + BernoulliB[n-1]; c[0] = 0; c[1] = 1; c[2] = 5/2; a[n_] := c[n] // Denominator; Table[a[n], {n, 0, 33}] (* _Jean-François Alcover_, Apr 15 2013 *)
%K A172031 nonn,frac
%O A172031 0,3
%A A172031 _Paul Curtz_, Jan 23 2010
%E A172031 Edited and extended by _R. J. Mathar_, Mar 14 2010