Number of ways to use the elements of {1,..,k}, 0<=k<=2n, once each to form a collection of n (possibly empty) sets, each with at most 2 elements.

A105748

Number of ways to use the elements of {1,..,k}, 0<=k<=2n, once each to form a collection of n (possibly empty) sets, each with at most 2 elements.

Terms

    a(0) =1a(1) =3a(2) =10a(3) =47a(4) =313a(5) =2744a(6) =29751a(7) =383273a(8) =5713110a(9) =96673861a(10) =1830257967a(11) =38326484944a(12) =879473289521

External references