Freaks City

Problem Analysis Given (n) where (1 \le n \le 20), we need to count the number of ways to completely cover the interval ([1, n]) using segments where each segment connects two coprime numbers. First, preprocess all coprime pairs ({a, b}) where (\gcd(a, b) = 1) and (a < b). Note that ({1, 1}) is excluded. When (n = 20), there are exactly 127 ...