A prime number is a natural number greater than 1 that has no divisors other than 1 and itself. Primes are the fundamental building blocks of all integers — every integer > 1 is either prime or can be uniquely factored into primes (Fundamental Theorem of Arithmetic).
Pro Tip
Quick primality checks: if a number ends in 0, 2, 4, 5, 6, 8 — it's not prime (except 2 and 5). Then check divisibility by 3 (digit sum divisible by 3) and 7. If it passes all these, it's likely prime if it's under 200.
Did You Know?
RSA encryption — used to secure most internet traffic including HTTPS — relies on the fact that multiplying two large primes is easy, but factoring the result back is computationally infeasible. The security of your bank's website depends on prime numbers.
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