Number of chains in power set of n-set.

Terms

a(0) =1a(1) =3a(2) =11a(3) =51a(4) =299a(5) =2163a(6) =18731a(7) =189171a(8) =2183339a(9) =28349043a(10) =408990251a(11) =6490530291a(12) =112366270379