Given an array, find the number of increasing sub-sequences having GCD=1 Example: A={1, 2, 3} Output: 5 The increasing sub-sequences are {1},{1,2},{1,2,3},{1,3},{2,3} The only approach I can think is to try all the possible sub-sequences and calculate their GCD.
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UPD: contest is over, if you know how to solve this task, I'd like to know either.
This problem was earlier discussed in another blog 1-2 weeks back on CF.
Constraints were small, so dpij = number of LIS ending at i with GCD j.
Things will be more clear with a recurrence.