Number of circular permutations of the multiset {1,1,2,2,...,2n,2n} (up to rotations) with even distances between equal elements.

A137749

Number of circular permutations of the multiset {1,1,2,2,...,2n,2n} (up to rotations) with even distances between equal elements.

Terms

    a(0) =1a(1) =30a(2) =13560a(3) =27785520a(4) =162030637440

External references