## Maximal coprime subset

### Problem 355

Published on Sunday, 23rd October 2011, 10:00 am; Solved by 334; Difficulty rating: 70%
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).