Number of distinct subsets S of [1..n] such that for all 1 <= k <= n, there exists two elements x,y in S (not necessarily distinct) such that x+y = 2k.

A383968

Number of distinct subsets S of [1..n] such that for all 1 <= k <= n, there exists two elements x,y in S (not necessarily distinct) such that x+y = 2k.