摘要：
原题链接 题意：求 \(\sum _{x = 0}^{m-1}[gcd(a, m) = gcd(a + x, m)]\) 题解：\(d = gcd(a, m)\) 然后发现 \(gcd(a, m) = gcd(\frac{a}{d}, \frac{m}{d})\) 并且 \((a+m) \mod m 阅读全文
摘要：
\(\varphi (x) = p_1^{k1-1} (p_1-1) \times p_2^{k2-1} (p2-1) \times p_3^{k3-1}(p3-1)\) \(\varphi (x) =x \times \frac{(p_1-1)}{p_1} \times \frac{(p_2-1) 阅读全文