Number of permutations of 1..n with i-9<=p(i)<=i+4.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =120a(5) =600a(6) =3000a(7) =15000a(8) =75000a(9) =375000a(10) =1776696a(11) =8208474a(12) =37712866a(13) =174397531a(14) =817232461a(15) =3852954960a(16) =18199500712a(17) =85943742360a(18) =405446385984