a(n) = T(n,n-2), array T as in A050143.

Terms

a(0) =1a(1) =7a(2) =32a(3) =160a(4) =832a(5) =4424a(6) =23872a(7) =130176a(8) =715520a(9) =3957448a(10) =21998176a(11) =122786976a(12) =687736896a(13) =3863423880a(14) =21758302848a(15) =122811081216a(16) =694533774336