G.f. A(x) satisfies A(x) = 1/(1 - x/(1 - x*A(x))^4).

Terms

a(0) =1a(1) =1a(2) =5a(3) =23a(4) =117a(5) =636a(6) =3607a(7) =21106a(8) =126489a(9) =772468a(10) =4789844a(11) =30075937a(12) =190851839a(13) =1222000222a(14) =7885041530a(15) =51222338580a(16) =334720178969