gives the number of permutations of n objects that leave no object fixed.
- Mathematical function, suitable for both symbolic and numerical manipulation.
- For non-integer n, the numerical value of Subfactorial[n] is given by Gamma[n+1, -1]/E.
- Subfactorial can be evaluated to arbitrary numerical precision.
- A permutation in which no object appears in its natural place is called a derangement.
- Subfactorial automatically threads over lists.
- Subfactorial gives 1.
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