G.f. A(x) satisfies A(x) = 1 + x*(1-x^3)^3*A(x)^2.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =11a(5) =30a(6) =87a(7) =264a(8) =830a(9) =2666a(10) =8710a(11) =28836a(12) =96514a(13) =326030a(14) =1110102a(15) =3805893a(16) =13127190a(17) =45520316a(18) =158600175a(19) =554948647a(20) =1949261610a(21) =6870665634a(22) =24294228065a(23) =86151877110a(24) =306323342082