All tools › Primes and factors
Prime number checker and factoriser
Prime or not, the factorisation, every divisor — and it says when the answer is probable rather than proved.
It runs entirely in this browser tab: what you type is never uploaded, and the tool makes no network request while it works. Open your browser's network panel and try it — nothing leaves the page. There is no sign-up and no limit beyond what your own browser can hold.
Settings
- List the divisors
- Every one of them, in order — or a count when there are more than the limit below.
- Nearest primes
- The one below and the one above, whether the number itself is prime or not.
- At most this many
- A number chosen to be divisible has thousands, and a cell with thousands of numbers in it is not an answer. A number from 1 to 4096.
How to use it
- Paste your text into the box above, or open a file.
- Adjust the settings beside it until the result is what you wanted.
- Copy the result, or save it as a file. The result updates as you type.
Questions
- Is what I type uploaded anywhere?
- No. This page carries the whole tool as WebAssembly and runs it on your own device. Nothing you type is sent anywhere, and there is no network request to make while it works.
- How exact is the arithmetic?
- Exact, in decimal, for everything the tool was given: no value here is put through floating point on the way to the answer. Where there is a genuine ceiling — thirty-nine digits for the number-theory tools, a fixed number of places for a repeating fraction — the tool says the limit rather than quietly truncating.
- Can I get this result again later?
- The settings travel in the page's address, after the #, so a link reproduces them exactly — and the fragment of an address is never sent to a server. Your last settings are also remembered on this device, which is worth knowing before you paste a number you would not want left there.
- Is there a version that is not a web page?
- Yes. The same tools are built as a desktop application from the same code, with a save dialog instead of a download and no network code at all.
Other tools for primes and factors
GCD and LCM calculator
Both, for as many numbers as you give, with Euclid's working written out step by step.
Factorial calculator
The exact value, however many digits that takes — which is the one thing a pocket calculator cannot give.
All thirty-one tools