Number of permutations of 1..n with i-9<=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) =98304a(10) =380094a(11) =1455278a(12) =5590035a(13) =21674069a(14) =84319556a(15) =328215940a(16) =1277085588a(17) =4967343120a(18) =19314847344a(19) =75083658528a(20) =291820729296