Number of partitions of {1..2n} that are invariant under a permutation consisting of n 2-cycles.

A002872

Number of partitions of {1..2n} that are invariant under a permutation consisting of n 2-cycles.

Terms

    a(0) =1a(1) =2a(2) =7a(3) =31a(4) =164a(5) =999a(6) =6841a(7) =51790a(8) =428131a(9) =3827967a(10) =36738144a(11) =376118747a(12) =4086419601a(13) =46910207114a(14) =566845074703

External references