Number of permutations of 1..n with i-8<=p(i)<=i+3.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =96a(5) =384a(6) =1536a(7) =6144a(8) =24576a(9) =93930a(10) =354106a(11) =1340251a(12) =5136061a(13) =19769184a(14) =76139584a(15) =293044020a(16) =1127167248a(17) =4333312848a(18) =16652629776a(19) =63980000904a(20) =245801168580a(21) =944477073376