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

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =30a(5) =76a(6) =197a(7) =520a(8) =1398a(9) =3820a(10) =10594a(11) =29768a(12) =84620a(13) =243000a(14) =704045a(15) =2055760a(16) =6043750a(17) =17875020a(18) =53148310a(19) =158773320a(20) =476311940a(21) =1434313960a(22) =4333867170a(23) =13135533552a(24) =39924668220a(25) =121661345656a(26) =371612931492