Prime Factorization · GCD · LCM
Everyday
Enter one or two positive integers. For each: the prime factorization in `p^e × q^f` form, every divisor, and whether the number itself is prime. Enter both and you also get GCD (greatest common divisor — useful for reducing fractions) and LCM (least common multiple — useful for finding a common period). Trial division up to √n is fast enough for numbers up to ~10¹² and runs entirely in your browser.
GCD (greatest common divisor)
36
LCM (least common multiple)
2520
360
Prime factorization
2^3 × 3^2 × 5
Divisors (24)
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120, 180, 360
252
Prime factorization
2^2 × 3^2 × 7
Divisors (18)
1, 2, 3, 4, 6, 7, 9, 12, 14, 18, 21, 28, 36, 42, 63, 84, 126, 252
Trial division up to √n. Fast for inputs up to ~10¹². Divisor scan is skipped above 10⁹ to stay snappy.
How to use
- Enter a number in field A for factorization, divisors, and primality.
- Add a second number in field B to also compute GCD and LCM.
- Copy the factorization or read the divisor list. Divisor list capped at first 200 for very composite numbers.
Frequently asked questions
- What's the largest input?
- Up to about 10¹² (a trillion). Above that, JavaScript loses integer precision (Number.MAX_SAFE_INTEGER is 2⁵³ ≈ 9×10¹²), and trial division to √n starts getting slow. For bigger numbers you'd need BigInt and Pollard's rho.
- Why no divisor list for large numbers?
- We cap the divisor scan at n < 10⁹ to avoid pegging your CPU. The prime factorization still runs because it's O(√n) by the largest prime factor, often much less than n itself.
- What's GCD good for?
- Reducing fractions: 252/360 = ?. GCD(252, 360) = 36, so 252/360 = 7/10. Also used in cryptography (RSA), and to determine whether two cycles will ever align.
- Is LCM(a, b) = a × b / GCD(a, b)?
- Yes, always, for positive integers. We use exactly that identity. The intuition: LCM has every prime factor at its highest power across a and b; GCD has every prime factor at its lowest power; multiplying recovers a × b.
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