G.f. A(x) satisfies: 1 + x = Product_{n>=1} (1 - (-x)^n*A(x)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =9a(6) =20a(7) =45a(8) =102a(9) =235a(10) =550a(11) =1304a(12) =3121a(13) =7526a(14) =18268a(15) =44610a(16) =109531a(17) =270240a(18) =669636a(19) =1665754a(20) =4158199a(21) =10413245a(22) =26153824a(23) =65864037a(24) =166277350a(25) =420733826a(26) =1066837944a(27) =2710448161a(28) =6898855337a(29) =17589508171