ppp 是一个奇质数，求证：
∑i=1p−1ip−1≡(p−1)!+p(mod p2)\sum_{i=1}^{p-1}i^{p-1}\equiv(p-1)!+p(\mod p^2)∑i=1p−1ip−1≡(p−1)!+p(modp2)
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