G.f. satisfies A(x) = 1 + x*A(x)^2*(1 + x^3*A(x)^2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =15a(5) =48a(6) =160a(7) =549a(8) =1929a(9) =6909a(10) =25134a(11) =92612a(12) =344924a(13) =1296376a(14) =4910656a(15) =18728645a(16) =71857133a(17) =277160183a(18) =1074085446a(19) =4180057725a(20) =16329796959a(21) =64014638564a(22) =251734985808a(23) =992788252700