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On the problem of mathematical permutation number formula, a-n-m (subscript n, superscript m) = n! Divided by (n-m)! Why? Detailed derivation process, I have not learned this formula, permutation and permutation number, but I still do not know the meaning of this formula, do not know what the formula is? How does the formula of anm = n · (n-1) · (n-2) · (n-3) ···· 3x2x1 come from,
N objects in a row of M boxes (M
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