Combinatorics Calculator

Count arrangements and selections of items. Given a total of n items and a choice of r, this computes permutations (ordered, P(n,r)), permutations with repetition (n^r), combinations (unordered, C(n,r)), combinations with repetition (multisets, C(n+r−1,r)), and the factorial of n. All arithmetic uses big integers, so the results are exact — even for values like C(100,50) that overflow ordinary floating point. Everything runs locally in your browser.