a(n) = [x^n] (1 - 4*x)^(-n/2)*x/(1 - x).

Terms

a(0) =0a(1) =1a(2) =5a(3) =37a(4) =313a(5) =2811a(6) =26093a(7) =247311a(8) =2377905a(9) =23104441a(10) =226289605a(11) =2230309533a(12) =22093913449a(13) =219786279909