Test whether a whole number is prime, see the first factor when it is not, and review the divisibility logic used for the result.
Supports large integers with `BigInt`, so values are not limited to normal JavaScript number precision.
No divisors were found from 2 through 9.
A prime number has exactly two positive divisors: 1 and itself. This checker rejects values smaller than 2, handles 2 as a special case, then tests only odd divisors.
It stops at the integer square root of the input. If no factor exists up to that point, a larger matching factor cannot exist without a smaller paired factor.
No. A prime number must have exactly two positive divisors. The number 1 has only one positive divisor: itself.
If a number has a factor larger than its square root, the paired factor must be smaller than the square root, so it would already have been found.
No. Prime numbers are defined in the positive integers greater than 1.
Yes. Trial division is simple and reliable, but large odd integers with no small factors require more checks before the result is known.
All even numbers greater than 2 are composite.
Every composite number can be written as a product of prime numbers.
Prime checks show up in cryptography, hashing strategies, and number theory exercises.
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