Number of permutations satisfying i-2<=p(i)<=i+5, i=1..n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =18a(4) =54a(5) =162a(6) =454a(7) =1267a(8) =3613a(9) =10344a(10) =29572a(11) =84436a(12) =240868a(13) =686884a(14) =1959636a(15) =5592181a(16) =15957717a(17) =45533682a(18) =129922090a(19) =370708166a(20) =1057755082a(21) =3018154342a(22) =8611878218a(23) =24572725639a(24) =70114579881a(25) =200061418144a(26) =570845362600