T(2n,n), T given by A026568.

Terms

a(0) =1a(1) =1a(2) =7a(3) =19a(4) =103a(5) =341a(6) =1809a(7) =6336a(8) =33899a(9) =121483a(10) =656199a(11) =2381512a(12) =12957809a(13) =47419503a(14) =259395664a(15) =954961034a(16) =5245001951a(17) =19397198595a(18) =106871608053