Math & Crypto
Prime Number Checker
Key in a number to see whether it’s prime and where it sits in the ordered list of primes (2 is #1).
Good for quick checks and building intuition. Light in-browser math, up to 1,000,000.
Result
17 is prime ✅
Prime index: #7 Nearest primes: 13, 19 Mersenne: no
History of prime numbers
Primes are the building blocks of integers—only divisible by 1 and themselves. Euclid proved there are infinitely many primes over 2000 years ago. Modern crypto (RSA, Diffie-Hellman, ECC variants) relies on prime properties for security.
Fun fact: the Prime Number Theorem shows primes thin out roughly like n / ln(n). Mersenne primes (2^p − 1 with p prime) are rare and power projects like GIMPS hunt for them. Primality tests are now fast (e.g., Miller–Rabin, AKS), making “is this prime?” almost instant for huge numbers.