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 A206820 #12 Jan 26 2014 11:56:08 %S A206820 1,1,3,42,914,23694,1048542,45379878,3272115926,257662344206, %T A206820 27726935045366,3101635433302996,474878584235678020, %U A206820 76786899439922296204,15844064187141655171020,3326909755872288926885670,897661138669999282018222470,246381314116108359863665821750 %N A206820 a(n) is the sum of the squares of the sizes of the conjugacy classes in the symmetric group A_n. %C A206820 a(n) is the sum over all elements of Alt_n of the size of their conjugacy class. Each conjugacy class is thus counted as many times as its size, giving a sum of squares. %e A206820 For n=5, a(5) = 1 + 12^2 + 12^2 + 15^2 + 20^2 = 914. %e A206820 The class equation of A_5 is 1 + 12 + 12 + 15 + 20 = 60 = 5!/2 %o A206820 (GAP) A206820 := n -> Sum(ConjugacyClasses(AlternatingGroup(n)), c->Size(c)^2); # _Eric M. Schmidt_, Jan 26 2014 %Y A206820 A087132 (sequence for S_n), A000702 (conjugacy classes in A_n) %K A206820 nonn,nice,easy %O A206820 1,3 %A A206820 _Olivier Gérard_, Feb 12 2012 %E A206820 More terms from _Eric M. Schmidt_, Jan 26 2014