a(n) = A027052(n, 2n-3).

Terms

a(0) =0a(1) =2a(2) =6a(3) =18a(4) =52a(5) =146a(6) =406a(7) =1126a(8) =3124a(9) =8684a(10) =24202a(11) =67640a(12) =189576a(13) =532786a(14) =1501254a(15) =4240550a(16) =12005780a(17) =34063896a(18) =96844082a(19) =275848044a(20) =787104288a(21) =2249633916a(22) =6439678858a(23) =18460717684a(24) =52994100984a(25) =152323413890a(26) =438363476086