a(n) = (n! - 2^n)/8, n >= 4.

Terms

a(0) =1a(1) =11a(2) =82a(3) =614a(4) =5008a(5) =45296a(6) =453472a(7) =4989344a(8) =59874688a(9) =778376576a(10) =10897284352a(11) =163459291904