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🔢 Prime Number Checker
Enter a number to check if it’s prime using a fast trial-division test.
Prime Number Checker
Check if a number is prime, see its divisors if it isn’t, and find the nearest prime numbers for quick reference.
✅ Prime
Nearest primes: 89, 101
How to use this tool
- Enter an integer and instantly learn whether it is prime.
- Review the divisor list when the number is composite to understand its factors.
- Check the nearest primes to guide rounding in cryptography or math lessons.
Why it helps
- Quickly vet candidate primes when implementing RSA-style key generation.
- Create math worksheets by generating composite numbers and listing their factors.
- Explore prime gaps by iterating through large inputs and comparing neighbor distances.
Limitations
- This deterministic check suits small to mid-sized integers. Extremely large values require probabilistic tests.
- Input is clamped to integers—decimals are rounded down before evaluation.
- Divisor enumeration stops after 50 checks to keep the UI responsive.
FAQ
- Does it handle big integers?
- Values within JavaScript’s safe integer range work well. For cryptographic primes larger than 2^53, use specialized libraries.
- Why are there limited divisors listed?
- To keep things fast, the tool shows small factors first. For exhaustive factorization, use a dedicated factoring utility.
- Can I test negative numbers?
- Negative inputs return not prime. Prime definitions apply to positive integers greater than 1.
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