Prime Number Checker

Sobre Prime Number Checker

This checker tells you whether a number is prime. Enter one number or a whole list, separated by spaces, commas or semicolons, and each is tested in turn. A prime is shown with the next prime after it, and any other number is shown with the prime factors that multiply together to make it, such as 84 as 2 × 2 × 3 × 7.

A prime is a whole number greater than 1 whose only factors are 1 and itself. Numbers up to one trillion are checked in an instant, by trying possible divisors up to the square root of the number. You can check up to 100 numbers at a time, each as a whole number of up to 13 digits. Results use commas to group the digits, so large numbers are easy to read.

Entries that are not whole numbers, such as negative numbers, decimals or words, are not guessed at. The tool names the first entry it could not read and stops, so you can correct it and try again. Zero and 1 are reported as not prime, with a note that primes start at 2.

Cómo usar Prime Number Checker

1. Type one or more whole numbers, separated by spaces, commas or semicolons.
2. Read whether each is prime, one result per line.
3. Use the next prime or the list of prime factors shown beside it.
4. Copy the results if you need them elsewhere.

Usos habituales

• Checking a number for a maths exercise or homework answer
• Finding the prime factors of a number, for example when simplifying a fraction
• Finding the next prime for a hash table size or a modulus
• Checking a whole list of numbers at once, such as a column of identifiers
• Choosing coprime values for a puzzle, a rota or a gear ratio
• Settling an argument about whether a number such as 91 is prime (it is not: it is 7 × 13)