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[数论] SOP10——$d(n)+\varphi(n)=2020$

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业余的业余 posted 2020-7-4 20:48 |Read mode
求所有的正整数 $n$, 使得\[d(n)+\varphi(n)=2020.\]其中,$d(n)$ 表示正整数 $n$ 的正约数的个数,$\varphi(n)$ 表示 $1,2,\cdots,n$ 中与 $n$ 互素的数的个数。

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hbghlyj posted 2023-5-15 19:43

$n\le1010$

MSE
$ϕ(n)+σ(n)≥2n$ for all positive integers $n$

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