Check if a number is prime and see its prime factors.
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How to use Prime & Factors
Open the Prime & Factors tool.
Paste or type your number into the input field.
The output updates as you type. Adjust the options if you need a different format.
Copy the result, or share the URL to hand the exact input to someone else.
About Prime & Factors
Test whether a number is prime and, if not, break it into its prime factorization (e.g. 360 = 2³ × 3² × 5). It also reports the divisor count and the next and previous primes. Factoring is instant for numbers up to about 100 trillion.
What people use it for
Check whether a number is prime.
Find the prime factorization of an integer.
Locate the nearest primes above and below a value.
Frequently asked questions
How big a number can it factor?
Up to about 10^14 (100 trillion) using trial division, which stays instant in the browser.
What else does it report?
Whether it's prime, the prime factorization, the total number of divisors, and the next and previous primes.
Is it private?
Every calculation happens on this page, in your own browser. Your input is never sent to a server and never logged, which also means the tool keeps working when you are offline.