T(2n,n+1), T given by A026747.

Terms

a(0) =1a(1) =5a(2) =22a(3) =95a(4) =411a(5) =1790a(6) =7855a(7) =34725a(8) =154573a(9) =692450a(10) =3120206a(11) =14135555a(12) =64356345a(13) =294341325a(14) =1351889910a(15) =6233399525a(16) =28845511125a(17) =133933280000a(18) =623811120960