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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =6a(6) =10a(7) =21a(8) =48a(9) =103a(10) =219a(11) =489a(12) =1114a(13) =2517a(14) =5712a(15) =13152a(16) =30492a(17) =70812a(18) =165165a(19) =387456a(20) =912378a(21) =2154250a(22) =5102343a(23) =12123027a(24) =28878384a(25) =68947041a(26) =164979006a(27) =395604531a(28) =950428335a(29) =2287387152