Results are for informational purposes only. All calculations are performed locally in your browser.
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Instantly check whether any number is prime or composite — up to 200 digits. Get the full factor list, prime factorization, nearest primes, and a divisibility chart. Check multiple numbers at once in Batch mode, or find every prime in a range. All results are calculated privately in your browser.
Results are for informational purposes only. All calculations are performed locally in your browser.
A prime number is a whole number greater than 1 that can only be divided evenly by 1 and itself. For example, 7 is prime because nothing other than 1 and 7 divides into it without a remainder. The first few primes are 2, 3, 5, 7, 11, and 13. Numbers with more than two factors — such as 6, which divides by 1, 2, 3, and 6 — are called composite numbers.
No. By definition, a prime number must have exactly two distinct factors: 1 and itself. The number 1 has only one factor, so it does not qualify. It is classified as neither prime nor composite — a special category all its own.
A composite number is a whole number greater than 1 that has at least one factor other than 1 and itself. For example, 15 is composite because it is divisible by 3 and 5 in addition to 1 and 15. Every composite number can be expressed as a unique product of prime factors — this is known as its prime factorization.
Twin primes are pairs of prime numbers that differ by exactly 2. Common examples include 3 and 5, 11 and 13, 17 and 19, and 29 and 31. They are special because primes generally become more spread out as numbers get larger — yet twin prime pairs keep appearing. When you check a prime number, this tool will tell you whether it belongs to a twin prime pair.
Prime numbers are sometimes called the building blocks of all whole numbers, because every number can be broken down into a unique product of primes. Beyond mathematics education, they play a central role in securing the internet. Modern encryption relies on the fact that it is easy to multiply two large primes together, but extraordinarily difficult to reverse the process and find the original primes from the result.
Yes. All calculations happen entirely within your browser. The numbers you enter are never sent to any server and never leave your device.