Number of permutations p of the multiset {0,0,1,1,2,2,...,n,n} such that p(1) = 0, p(2n+2) = n, and |p(i) - p(i-1)| is always 1 or 2.

A375092

Number of permutations p of the multiset {0,0,1,1,2,2,...,n,n} such that p(1) = 0, p(2n+2) = n, and |p(i) - p(i-1)| is always 1 or 2.

Terms

    a(0) =1a(1) =4a(2) =24a(3) =78a(4) =300a(5) =1248a(6) =4957a(7) =19372a(8) =76895a(9) =305672a(10) =1209771a(11) =4789866a(12) =18985256a(13) =75228302a(14) =298018487a(15) =1180748188a(16) =4678314418a(17) =18535510324a(18) =73437503198a(19) =290961862062

External references