Main diagonal of triangle in A333282.

Terms

a(0) =4a(1) =56a(2) =624a(3) =3288a(4) =16912a(5) =51864a(6) =164692a(7) =422792a(8) =1023416a(9) =2101272a(10) =4387296a(11) =8214688a(12) =15485996