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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =6a(6) =16a(7) =36a(8) =75a(9) =163a(10) =391a(11) =991a(12) =2498a(13) =6150a(14) =15016a(15) =37116a(16) =93482a(17) =238154a(18) =608074a(19) =1551370a(20) =3964200a(21) =10176384a(22) =26261500a(23) =68034484a(24) =176661828a(25) =459534596a(26) =1197777556a(27) =3129475636a(28) =8195867902a(29) =21508247446