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 A218913 #24 Mar 20 2020 10:41:51 %S A218913 1,1,2,4,8,13,21,31,49,74,113,139,216,268 %N A218913 Number of distinct orders of subgroups of the symmetric group. %H A218913 L. Naughton and G. Pfeiffer, <a href="http://arxiv.org/abs/1211.1911">Integer sequences realized by the subgroup pattern of the symmetric group</a>, arXiv:1211.1911 [math.GR], 2012-2013 and <a href="https://cs.uwaterloo.ca/journals/JIS/VOL16/Naughton/naughton2.html">J. Int. Seq. 16 (2013) #13.5.8</a> %H A218913 Liam Naughton, <a href="http://www.maths.nuigalway.ie/~liam/CountingSubgroups.g">CountingSubgroups.g</a> %H A218913 Liam Naughton and Goetz Pfeiffer, <a href="http://schmidt.nuigalway.ie/tomlib/">Tomlib, The GAP table of marks library</a>, %o A218913 (GAP) %o A218913 Size(DuplicateFreeList(List(ConjugacyClassesSubgroups(G), x-> Size(Representative (x))))); %o A218913 (Sage) %o A218913 def A218913(n): %o A218913 G = SymmetricGroup(n) %o A218913 subgroups = G.conjugacy_classes_subgroups() %o A218913 return len(set(subG.cardinality() for subG in subgroups)) %o A218913 # _Peter Luschny_, Apr 21 2016 %K A218913 nonn,more %O A218913 0,3 %A A218913 _Liam Naughton_, Nov 09 2012