Number of permutations of 1..n with i-5<=p(i)<=i+4.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =120a(5) =600a(6) =2616a(7) =10554a(8) =41506a(9) =164731a(10) =673261a(11) =2784240a(12) =11528872a(13) =47561640a(14) =195350784a(15) =800662464a(16) =3282217584a(17) =13467670528a(18) =55304280616a(19) =227170084693a(20) =933011493125