Test If a Number Is a Prime
Check if an integer is prime. Runs entirely in your browser, so your data never leaves your device.
0 chars · 0 lines
Output
The result appears here as you type.
How to use Test If a Number Is a Prime
- 1. Paste your numbers. Enter one integer per line to check. Each number is tested independently, so you can check several candidates in a single batch.
- 2. Read the primality result. The output states whether each number is a prime, or names a divisor if it is not, giving you the reason a composite number failed the test.
- 3. Copy the results. Copy the output list into a homework answer, a filtered dataset, or a script that needs a verified list of primes and composites.
When to use Test If a Number Is a Prime
Test If a Number Is a Prime checks a batch of integers for primality and, when a number fails, reports a divisor that proves it composite. Use it whenever you need a quick, verified answer instead of trial-dividing by hand.
- Checking a large candidate number by hand. You are working through a number theory problem with a large candidate like 97 or 101 and want to confirm primality quickly instead of testing every divisor up to its square root manually.
- Verifying a primality-testing algorithm. You implemented a primality test, like trial division or the Miller-Rabin test, and want a trusted set of known primes and composites to check your function's output against.
- Filtering a list of numbers for a math puzzle. A puzzle requires identifying which numbers in a given list are prime before applying a further rule, and batch-testing the whole list here is faster than checking each one individually.
- Finding the divisor that disqualifies a composite number. You want to know not just that a number is not prime but which specific factor proves it, useful when explaining to a student exactly why a number like 91 fails the primality test.
Examples
Test a few numbers
Input
97 98
Output
97 is a prime 98 is not a prime (divisible by 2)
About the Test If a Number Is a Prime tool
Test If a Number Is a Prime runs as plain JavaScript in your browser tab, with no server behind it. Check if an integer is prime. Whatever you put in stays on your device from start to finish.
The tool is part of EditSafely's Math Tools section, 234 single-purpose utilities built around the same idea: open the page, get the result, keep your data to yourself.
There is nothing to configure. Provide the input and the result appears on its own. A worked example further down the page shows exactly what the tool produces for a real input.
That local-first design has practical benefits beyond privacy. The tool keeps working on a flaky connection once the page has loaded, results are instant because nothing round-trips to a server, and it is safe to use with confidential material.
Frequently asked questions
Does Test If a Number Is a Prime cost anything?
Yes, it is completely free. All 2,658 tools on EditSafely work without an account, a subscription or usage limits.
Is it safe to paste sensitive or confidential data?
No data leaves your device. The whole tool is JavaScript that runs inside your browser tab, so there is no upload, no server-side processing and no log of what you did. If you disconnect from the internet after the page loads, it keeps working.
How much text can I process at once?
There is no fixed limit. Because the work happens on your own device rather than on a shared server, the practical ceiling is your machine's memory, which comfortably handles inputs far larger than typical online tools allow.
Do I need to sign up or install anything?
Nothing to install and no account needed. Open the page in any up-to-date browser, including on a phone or tablet, and the tool is ready.
How do I use the result?
The output panel has a one-click copy button, and you can keep refining the input while you work; the result updates in place as you type.