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

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =9a(5) =21a(6) =53a(7) =155a(8) =449a(9) =1273a(10) =3721a(11) =11155a(12) =33529a(13) =101245a(14) =309037a(15) =950587a(16) =2936833a(17) =9117169a(18) =28448209a(19) =89134435a(20) =280252585a(21) =884123429a(22) =2797933733a(23) =8879167067a(24) =28249550913a(25) =90091462761a(26) =287946752601a(27) =922194331891