How to use it

Put a whole number in n, and (for the middle two buttons) a second whole number in r. Then pick a button.

The buttons

• n! — factorial: n × (n−1) × … × 1. The number of ways to order n things.
• nPr — permutations: ways to pick r things from n when order matters.
• nCr — combinations: ways to pick r things from n when order doesn't matter. (52 and 5 = poker hands.)
• circular — ways to seat n things in a ring.

What it can do

Every answer is exact with no rounding, no matter how many digits · handles enormous n (100000! appears in a couple of seconds).

What it can't do

Whole numbers only — no decimals or fractions. For nPr and nCr, r can't be bigger than n. It counts arrangements; it doesn't list them.