G.f. A(x) satisfies: 1 = Sum_{n>=0} x^n / A(x)^(n+1) * Product_{k=1..n} (1 + k*x).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =3a(7) =8a(8) =17a(9) =48a(10) =128a(11) =380a(12) =1157a(13) =3660a(14) =12096a(15) =40792a(16) =143065a(17) =511012a(18) =1882800a(19) =7070528a(20) =27218600a(21) =106809732a(22) =427962654a(23) =1746800424a(24) =7262220721a(25) =30724381288a(26) =132185762998a(27) =578077437072