E.g.f.: Product_{n>=1} 1/(1 - x^n/n!)^n.

Terms

a(0) =1a(1) =1a(2) =4a(3) =15a(4) =82a(5) =475a(6) =3456a(7) =26719a(8) =239996a(9) =2313609a(10) =24846640a(11) =285861301a(12) =3586817928a(13) =47988744115a(14) =690525294018