G.f. satisfies A(x) = 1 + x*A(x) / (1 - x^3*A(x)^4).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =7a(6) =22a(7) =58a(8) =142a(9) =363a(10) =1014a(11) =2966a(12) =8645a(13) =24824a(14) =71189a(15) =206742a(16) =609159a(17) =1809493a(18) =5388804a(19) =16073002a(20) =48092377a(21) =144532884a(22) =436168716a(23) =1320372837a(24) =4006489208a(25) =12183544414a(26) =37132838866a(27) =113426618425a(28) =347191793705