Enter the total n and the number chosen r, and the calculator returns both the permutations (nPr) and combinations (nCr).
Permutations (nPr) count ordered arrangements; combinations (nCr) count selections where order does not matter.
nPr = n! / (n−r)! and nCr = n! / (r!(n−r)!), where n is the total and r the number chosen.
It multiplies iteratively rather than computing huge factorials directly, avoiding overflow for large n.