T(2n,n+1), T given by A026769.

Terms

a(0) =1a(1) =4a(2) =16a(3) =66a(4) =281a(5) =1232a(6) =5548a(7) =25598a(8) =120724a(9) =580658a(10) =2842222a(11) =14129842a(12) =71212849a(13) =363242996a(14) =1872444764a(15) =9741516322a(16) =51092414488a(17) =269881127838