Number of ways to use the elements of {1,...,k}, 0 <= k <= 2n, once each to form a sequence of n sets, each having 1 or 2 elements.

A105749

Number of ways to use the elements of {1,...,k}, 0 <= k <= 2n, once each to form a sequence of n sets, each having 1 or 2 elements.

Terms

    a(0) =1a(1) =2a(2) =14a(3) =222a(4) =6384a(5) =291720a(6) =19445040a(7) =1781750880a(8) =214899027840

External references