Prime Checker
Check if a number is prime and find the nearest lower and upper prime numbers.
Run tool
Prime Checker tests any integer value to determine whether it is a prime number and pinpoints the closest prime numbers surrounding it. When you enter a value, the tool evaluates the integer value you enter to see whether it has factors other than one and itself. Whole numbers smaller than two are classified as non-prime, while two and three are recognized as the smallest primes. For numbers greater than two, the output identifies the preceding prime and the subsequent prime. When you evaluate a composite number, the summary also displays the exact numeric distances to both the nearest lower prime and the nearest upper prime. If you check numbers at or below two, the reported lower boundary defaults to two. This free online calculator offers an immediate way to explore number theory, verify homework equations, investigate factorization boundaries, and examine prime distributions across positive integers.
Instructions
- Enter the number you want to evaluate into the Number field.
- Click the calculate button to process the integer.
- Read the results panel to see the primality status, adjacent primes, and numeric distances.
Examples
- Enter 14: The tool marks 14 as not prime, reports 13 as the nearest lower prime (distance 1), and reports 17 as the nearest upper prime (distance 3).
- Enter 17: The tool identifies 17 as a prime number, reports 13 as the lower adjacent prime, and reports 19 as the upper adjacent prime.
FAQ
How are decimal inputs handled?
The tool evaluates the integer value you enter. If you type a decimal, only the whole number part is used.
Why are numbers below 2 reported as not prime?
In standard mathematics, prime numbers are integers strictly greater than 1 that have no positive divisors other than 1 and themselves. Consequently, 0, 1, and negative numbers are not prime.
What lower boundary is used for numbers at or below 2?
For inputs at or below 2, the lower reference value defaults to 2 rather than seeking a smaller prime.