Permutation and Combination Calculator
Calculate permutations P(n,r) and combinations C(n,r) for integers 0≤r≤n with factorial formulas. Example: n=5, r=2 → P=20, C=10. Browser-only counting process for order vs unordered picks.
How it works
Enter n and r. Factorials are computed iteratively.
Formula
P = n×(n−1)×…×(n−r+1); C = P / r!. Notes:
- r > n is rejected.
- Non-integers are rejected.
- Pair with quadratic / slope for algebra drills.
Example
Example: n=5, r=2 → P=20, C=10.
When to use it
- Counting problems.
- Homework P/C.
- Compare related algebra tools.
Frequently asked questions
Sample?
5P2=20, 5C2=10.
r>n?
Invalid.
Large n?
May lose precision in JS Number.
Advice?
Educational only.
Related tools
Questions or feedback
Something unclear, broken, or missing? Draft a message below — we read every note about these tools.