Coprimality Census
Challenge on lesson: Final 2-B: Coprimality Census
CHALLENGE
Difficulty: advanced+25 XP
**Problem.** Line 1: n. Line 2: n values. Print the number of pairs i < j with gcd(a[i], a[j]) == 1. **Constraints:** 1 <= n <= 100000; 1 <= a[i] <= 1e6. **R versus W.** The graded wrong solution counts every pair sharing any common divisor >= 2.
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