Number of permutations of 1..n with i-8<=p(i)<=i+2.

Terms

a(0) =1a(1) =2a(2) =6a(3) =18a(4) =54a(5) =162a(6) =486a(7) =1458a(8) =4374a(9) =12866a(10) =37831a(11) =111961a(12) =331804a(13) =983200a(14) =2913064a(15) =8629984a(16) =25563928a(17) =75720112a(18) =224270920a(19) =664246912a(20) =1967449976a(21) =5827579985a(22) =17261274041a(23) =51127661518a(24) =151439081294a(25) =448558789858