a(n) = A354650(n,2*n), for n >= 0.

Terms

a(0) =1a(1) =3a(2) =15a(3) =83a(4) =486a(5) =2937a(6) =18109a(7) =113220a(8) =715122a(9) =4552229a(10) =29156985a(11) =187683795a(12) =1213110600a(13) =7868238588a(14) =51184173036a(15) =333809308696