Math & Statistics
Double Factorial & Subfactorial Calculator
Compute the double factorial (n!!) and subfactorial (derangements, !n) of a number.
Your inputs
Change any value to update the result instantly.
Double factorial n!!
105
Subfactorial !n (derangements)
1,854
Regular factorial n!
5,040
Formula and working
n!! = n(n−2)(n−4)... · !n = n!·Σ(−1)ᵏ/k!
- 1
Substitute your values
n = 7
- 2
Apply the formula
n!! = n(n−2)(n−4)... · !n = n!·Σ(−1)ᵏ/k! = 105
Frequently asked questions
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
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