a(n) = A027082(n, 2n-3).

Terms

a(0) =1a(1) =3a(2) =9a(3) =28a(4) =84a(5) =246a(6) =714a(7) =2059a(8) =5917a(9) =16971a(10) =48633a(11) =139333a(12) =399267a(13) =1144669a(14) =3283839a(15) =9427981a(16) =27090715a(17) =77911897a(18) =224272499a(19) =646157234a(20) =1863317958a(21) =5377939756a(22) =15535195892a(23) =44913790501a(24) =129955421387a(25) =376313609029