Number of permutations of length n within distance 9.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =24a(5) =120a(6) =720a(7) =5040a(8) =40320a(9) =362880a(10) =3628800a(11) =33022080a(12) =277280640a(13) =2184341040a(14) =16427628720a(15) =119892387720a(16) =861175365144