PrimeOrNot – Prime Number Lab

Check whether a number is prime, inspect factors and explore prime-number guides from PrimeOrNot.com.

PrimeOrNot – Prime Number Lab gives you a fast way to check whether a positive integer is prime directly from the browser toolbar. Enter a number to see whether it is prime or composite, inspect its factorization, find nearby prime numbers and view the surrounding prime gap. Features • Check positive integers up to 15 digits • Identify prime and composite numbers • View prime factorization for composite numbers • Find the nearest prime below a number • Find the nearest prime above a number • View the surrounding prime gap • Recognize important edge cases • Open educational guides about prime numbers • Access prime-number reference and pattern guides • Keep a small list of recent checks locally on your device • Open the full PrimeOrNot.com checker for additional information The instant number check runs locally in the extension and does not require an account. PrimeOrNot is designed for students, teachers, developers, mathematics enthusiasts and anyone who needs a quick prime-number check while browsing. No account is required to use the extension.