Number of permutations of length n within distance 7.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =24a(5) =120a(6) =720a(7) =5040a(8) =40320a(9) =287280a(10) =1865520a(11) =11345160a(12) =66349464a(13) =381523758a(14) =2193664790a(15) =12764590275a(16) =75796724309a(17) =455383613924