# Problem 355: Maximal coprime subset
Define Co(n) to be the maximal possible sum of a set of mutually
co-prime elements from {1, 2, ..., n}. For example Co(10) is 30 and hits
that maximum on the subset {1, 5, 7, 8, 9}. You are given that Co(30) =
193 and Co(100) = 1356. Find Co(200000).