a(n) = T(2n,n+4), T given by A026725.

Terms

a(0) =1a(1) =10a(2) =67a(3) =379a(4) =1958a(5) =9576a(6) =45190a(7) =208084a(8) =941480a(9) =4204949a(10) =18597694a(11) =81635060a(12) =356220369a(13) =1547066801a(14) =6693361973a(15) =28868868733a(16) =124194904215a(17) =533156609953