Number of permutations of 1..n with i-7<=p(i)<=i+3.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =96a(5) =384a(6) =1536a(7) =6144a(8) =23118a(9) =85310a(10) =316275a(11) =1191989a(12) =4518164a(13) =17135188a(14) =64906836a(15) =245607600a(16) =928634304a(17) =3509372424a(18) =13260273636a(19) =50117434276a(20) =189468674404a(21) =716365025813