Avoiding Multiples of Seven
What is the largest possible size of a subset $S$ of {1, 2, ..., 50} such that no two distinct elements of $S$ have a sum divisible by 7? Give an integer.
Related problems & prerequisites
Worth solving first
- Hidden Progressions 5.0/10
- Differences of Squares 5.0/10
- Guaranteed Pair Sum 4.0/10
Source: Classic exercise in wide circulation; no traceable original source. Statement written for AxiomIQ.