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

Terms

a(0) =1a(1) =1a(2) =4a(3) =14a(4) =56a(5) =241a(6) =1080a(7) =4998a(8) =23704a(9) =114588a(10) =562552a(11) =2797138a(12) =14057140a(13) =71288385a(14) =364360204a(15) =1874960408a(16) =9706035408a(17) =50510552881a(18) =264096980192