T(2n,n-2), T given by A026681.

Terms

a(0) =1a(1) =11a(2) =50a(3) =352a(4) =1412a(5) =9012a(6) =35218a(7) =216556a(8) =841161a(9) =5080487a(10) =19727183a(11) =117977884a(12) =458783666a(13) =2727417052a(14) =10627866041a(15) =62938875136a(16) =245774605829