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Update sieve.md
author
Ir1dXD
<sirius.caffrey@gmail.com>
Fri, 23 Nov 2018 00:36:19 +0000
(08:36 +0800)
committer
GitHub
<noreply@github.com>
Fri, 23 Nov 2018 00:36:19 +0000
(08:36 +0800)
docs/math/sieve.md
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void init() {
上面的这种**线性筛法**也称为 **Euler 筛法**(欧拉筛法)。
+??? note
+ 注意到筛法求素数的同时也得到了每个数的最小质因子
+
## 筛法求欧拉函数
注意到在线性筛中,每一个合数都是被最小的质因子筛掉。比如设 $p_1$ 是 $n$ 的最小质因子,$n' = \frac{n}{p_1}$,那么线性筛的过程中 $n$ 通过 $n' \times p_1$ 筛掉。