Commit 0d826a50 authored by lihaoyu1234's avatar lihaoyu1234 Committed by Xeonacid
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Update euler.md (#1219)

parent 63823786
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    积性是什么意思呢?如果有 $\gcd(a, b) = 1$ ,那么 $\varphi(a \times b) = \varphi(a) \times \varphi(b)$ 。

    特别地,当 $n$ 是奇数时 $\varphi(2n) = 2 \times \varphi(n)$ 。
    特别地,当 $n$ 是奇数时 $\varphi(2n) = \varphi(n)$ 。

-    $n = \sum_{d | n}{\varphi(d)}$