E.g.f.: exp((1+x)*(1+x^2)*(1+x^3) - 1).

Terms

a(0) =1a(1) =1a(2) =3a(3) =19a(4) =97a(5) =681a(6) =5971a(7) =50443a(8) =512289a(9) =5821777a(10) =67968451a(11) =880345731a(12) =12230425153a(13) =177123301369