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数学

重复排列

Permutations Calculator

P(n,r) — order matters

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专业提示

License plate formats illustrate permutations with replacement: a plate with 3 letters + 3 digits has 26³ × 10³ = 17,576,000 combinations — enough for most states' vehicle fleets.

难度:中级

你知道吗?

A standard combination lock (3 numbers, 0–39) actually uses permutations WITH replacement: 40³ = 64,000 combinations. A determined thief can try all combinations in about 4 hours manually.

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Reviewed May 2026
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