Number of permutations of 1..n with i-7<=p(i)<=i+4.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =120a(5) =600a(6) =3000a(7) =15000a(8) =68856a(9) =302730a(10) =1315666a(11) =5767051a(12) =25794781a(13) =116409504a(14) =526500664a(15) =2378347800a(16) =10719053952a(17) =48224952000a(18) =216718943232a(19) =973508319552