Prime numbers are the building blocks of number theory and play a critical role in cryptography, computer science, and mathematics education. This prime number checker instantly determines whether any whole number is prime, divisible only by 1 and itself, or composite, and if composite, lists all of its factors. It also identifies the nearest prime numbers above and below your input, which is useful for exploring number patterns or solving math problems involving prime gaps. Students learning about factorization, programmers implementing number-theory algorithms, and curious minds alike will find instant, accurate answers with this tool.