G.f.: A(x) = 1 + x*A(x)^2/(1-x-x^2).

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =42a(5) =168a(6) =696a(7) =2965a(8) =12915a(9) =57276a(10) =257787a(11) =1174597a(12) =5407854a(13) =25119663a(14) =117579351a(15) =554053049a(16) =2626184688a(17) =12513029640a(18) =59898952650a(19) =287931365692