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

Terms

a(0) =1a(1) =0a(2) =1a(3) =2a(4) =4a(5) =12a(6) =30a(7) =84a(8) =238a(9) =680a(10) =1993a(11) =5882a(12) =17575a(13) =52976a(14) =160870a(15) =491924a(16) =1512940a(17) =4677672a(18) =14529744a(19) =45320640a(20) =141897039a(21) =445792908a(22) =1404899598a(23) =4440113940a(24) =14069493813a(25) =44689897200a(26) =142268117566a(27) =453839997836