Determine whether an integer greater than one has exactly two positive divisors. Its classification sits beside the working formula for a quick arithmetic check.
A prime number is an integer greater than one divisible only by one and itself. A composite number has at least one additional positive factor. For a connected concept in Prime Number Checker, see prime factorization.
On this page, the displayed classification follows this definition rather than any similarly named measure.
Reject divisibility by two, then try odd candidates no larger than the square root. Finding one exact divisor proves compositeness; exhausting the candidates proves primality.
Ninety-seven has no prime divisor at or below √97, which is less than ten. Testing 2, 3, 5, and 7 therefore proves that 97 is prime.
Primality checks support factorization, modular arithmetic, fraction reduction, and many counting arguments. Small primes also appear in cycle lengths and evenly spaced patterns.
One is neither prime nor composite. Negative integers are not prime under the usual definition, and a large probable prime requires stronger methods than casual trial division.
Record the source conventions for Prime Number; Prime Number still requires the reader to validate the setup for prime number checker.
Treat each labeled field as part of the definition, not merely an empty box. The field assignment determines what the displayed classification describes. Convert measured values to compatible units first and retain their original precision until the final rounding choice.
Changing an integer by one can switch its classification abruptly because primes are not evenly spaced. Predict that movement before recalculating the classification; disagreement points to an input-role or sign issue.
Report the classification at a precision justified by the inputs. A long browser decimal is computational detail, not evidence that the source values were measured that accurately. When an exact symbolic form is conventional, keep it beside the rounded value so later work is not forced to reuse an early approximation.
Prime factorization explains a composite input; this page answers only the yes-or-no primality question. Here the requested quantity is specifically classification.
Keep the supplied input with the result, including any units and the final rounding place. The displayed formula then preserves how the classification was obtained.
No.
Yes, and it is the only even prime.
A composite number must have at least one factor no larger than its square root.