G.f.: (2*x+1)/(2*sqrt(4*x^2-8*x+1)) + 1/2.

Terms

a(0) =1a(1) =3a(2) =15a(3) =90a(4) =579a(5) =3858a(6) =26262a(7) =181380a(8) =1265955a(9) =8906706a(10) =63058530a(11) =448716876a(12) =3206387790a(13) =22992276180a(14) =165364807308