G.f. A(x) satisfies A(x) = 1/Product_{k>0} (1-x^k*A(x)).

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =30a(5) =104a(6) =378a(7) =1414a(8) =5424a(9) =21208a(10) =84244a(11) =339008a(12) =1379173a(13) =5663078a(14) =23439651a(15) =97692524a(16) =409650348a(17) =1727034770a(18) =7315915371a(19) =31124324364a(20) =132926220818a(21) =569695276362