G.f. satisfies A(x) = 1+x + x^2*A(x)^6.

Terms

a(0) =1a(1) =1a(2) =1a(3) =6a(4) =21a(5) =86a(6) =396a(7) =1812a(8) =8607a(9) =41958a(10) =207333a(11) =1040234a(12) =5281965a(13) =27078756a(14) =140021248a(15) =729369474a(16) =3823598232a(17) =20158251814a(18) =106809280563a(19) =568471343322