a(n) is the number of abelian subgroups of maximal order in S_n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =7a(4) =10a(5) =10a(6) =245a(7) =280a(8) =280a(9) =14700a(10) =15400a(11) =15400a(12) =1401400a(13) =1401400a(14) =1401400a(15) =196196000a(16) =190590400a(17) =190590400a(18) =38022784800a(19) =36212176000a(20) =36212176000