Number of permutations p of [n] such that max_{j=1..n} |p(j)-j| = 2.

Terms

a(0) =0a(1) =3a(2) =9a(3) =23a(4) =60a(5) =151a(6) =366a(7) =877a(8) =2088a(9) =4937a(10) =11621a(11) =27285a(12) =63944a(13) =149652a(14) =349924a(15) =817712a(16) =1910027a(17) =4460139a(18) =10412815a(19) =24306706a(20) =56733689a(21) =132411638a(22) =309022917a(23) =721175422a(24) =1682988807a(25) =3927486177a(26) =9165229371a(27) =21387927668a(28) =49910484308a(29) =116469784820