G.f. Sum_{n>=0} Series_Reversion( x/(1+x)^n )^n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =25a(5) =129a(6) =784a(7) =5472a(8) =42993a(9) =374190a(10) =3564176a(11) =36808647a(12) =409067204a(13) =4861490200a(14) =61457674398a(15) =822732344816