Number of permutations p of [n] satisfying i-2 <= p(i) <= i+4 for all i in [n].

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =18a(5) =54a(6) =146a(7) =391a(8) =1081a(9) =3004a(10) =8320a(11) =22984a(12) =63424a(13) =175176a(14) =484113a(15) =1337721a(16) =3695886a(17) =10210702a(18) =28209954a(19) =77940078a(20) =215337554a(21) =594943087a(22) =1643728129a(23) =4541349672a(24) =12547013504a(25) =34665373744a(26) =95774808224a(27) =264610227072a(28) =731075061761