a(n) = T(2*n, n), array T as in A047080.

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =27a(5) =83a(6) =259a(7) =817a(8) =2599a(9) =8323a(10) =26797a(11) =86659a(12) =281287a(13) =915907a(14) =2990383a(15) =9786369a(16) =32092959a(17) =105435607a(18) =346950321a(19) =1143342603a(20) =3772698725a(21) =12463525229a(22) =41218894577a(23) =136451431723a(24) =452116980643