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Prime Checker, Factorizer, GCD & LCM

Primality, factorization, neighboring primes, ranges, and multi-number GCD/LCM — exact BigInt arithmetic, in your browser.
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Runs here in the tab · deterministic Miller-Rabin under ~3.3e24
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- Primality: trial division, then Miller-Rabin. Below ~3.3×10²⁴ the base set is deterministic — the answer is a fact. Above it, 40 random rounds run and the answer says probable prime, because that is what it is.
- Factorization: trial division, then Pollard's rho with a hard cap of 200,000 rounds. A number the cap cannot crack (typically a product of two large primes) refuses with the cap named — a wrong factor list would be worse. Every completed list is verified by multiplying back.
- Ranges sieve exactly (width ≤ 1,000,000 ); gcd/lcm are exact BigInt Euclid; lcm refuses a zero operand (meaningless by convention).
- Operands are digit strings up to 40 digits. Large work — sieves and factorizations past 10¹⁵ — runs in the math family worker.

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