A set having the largest number 
of distinct residue classes modulo 
so that no subset has zero sum.
Maximal Zero-Sum-Free Set
See also
Maximal Sum-Free SetExplore with Wolfram|Alpha
References
Guy, R. K. "Maximal Zero-Sum-Free Sets." §C15 in Unsolved Problems in Number Theory, 2nd ed. New York: Springer-Verlag, pp. 129-131, 1994.Referenced on Wolfram|Alpha
Maximal Zero-Sum-Free SetCite this as:
Weisstein, Eric W. "Maximal Zero-Sum-Free Set." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/MaximalZero-Sum-FreeSet.html