Permutation Calculator
Calculate P(n,r): the number of ordered arrangements of r items from n.
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Enter the total number of items (n) and how many to arrange (r). The calculator computes P(n,r) = n!/(n-r)!, where order matters. For example, P(10,3) = 720 means there are 720 ways to arrange 3 items chosen from 10.
About Permutations
A permutation counts the number of ways to arrange items where order matters. Selecting (A,B,C) is different from (C,A,B). Permutations are used in password counting, race finish orders, seating arrangements, and any scenario where sequence is significant.
Frequently Asked Questions
When do I use permutations vs combinations?
Use permutations when order matters (rankings, passwords). Use combinations when order does not matter (selecting a team).
What is P(n,n)?
P(n,n) = n!, the number of ways to arrange all n items. For example, P(5,5) = 120.
How large can n be?
JavaScript numbers overflow around 170!. This calculator handles up to n=170 precisely and uses log-factorials for larger values, though results become approximate.