a(n) = A027082(n, 2n-5).

Terms

a(0) =1a(1) =3a(2) =9a(3) =31a(4) =102a(5) =328a(6) =1035a(7) =3217a(8) =9880a(9) =30062a(10) =90803a(11) =272697a(12) =815228a(13) =2428298a(14) =7212179a(15) =21370921a(16) =63207913a(17) =186668355a(18) =550617011a(19) =1622604097a(20) =4777983482a(21) =14060981252a(22) =41360234037a(23) =121616984851a(24) =357510486913