Number of permutations satisfying i-2<=p(i)<=i+6, i=1..n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =18a(4) =54a(5) =162a(6) =486a(7) =1394a(8) =3991a(9) =11593a(10) =33772a(11) =98320a(12) =286072a(13) =831952a(14) =2418664a(15) =7030816a(16) =20441944a(17) =59441521a(18) =172843609a(19) =502580846a(20) =1461344622a(21) =4249102850a(22) =12354982862a(23) =35924300898a(24) =104456501102a(25) =303726483778a(26) =883140022543