T(2n,n-4), T given by A026747.

Terms

a(0) =1a(1) =15a(2) =141a(3) =1070a(4) =7187a(5) =44673a(6) =263431a(7) =1496218a(8) =8266100a(9) =44718596a(10) =238015318a(11) =1250656153a(12) =6504202391a(13) =33543967700a(14) =171810543570a(15) =875006817465