Number of permutations satisfying i-3<=p(i)<=i+5, i=1..n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =96a(5) =384a(6) =1374a(7) =4718a(8) =16275a(9) =57749a(10) =206756a(11) =739780a(12) =2637348a(13) =9378840a(14) =33318804a(15) =118439044a(16) =421340612a(17) =1499388117a(18) =5335199213a(19) =18980987054a(20) =67522942850a(21) =240204885524a(22) =854523535096