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

Terms

a(0) =1a(1) =1a(2) =4a(3) =13a(4) =32a(5) =147a(6) =460a(7) =1436a(8) =5662a(9) =17287a(10) =60644a(11) =209377a(12) =688370a(13) =2391256a(14) =8105590a(15) =27102666a(16) =92744010a(17) =312994179a(18) =1067043874a(19) =3659563265a(20) =12430287670a(21) =42225015449a(22) =143808001426a(23) =487301478188