Skip to content
OneKitly
Sign up · Sign in

Prime number checker

Check whether a number is prime and find its smallest divisor.

Related tools

All Numbers & arithmetic tools →
Prime factorization calculatorBreak a whole number down into the product of its prime factors.First n prime numbersList the first n prime numbers — the building blocks of arithmetic that have no divisors but 1 and themselves. Enter how many you want (up to 10,000) and it returns the sequence, the nth prime itself and the sum of them all.List of prime numbersList every prime number up to a chosen limit, using the Sieve of Eratosthenes. Enter an upper bound (up to 100,000) and it returns all primes at or below it, how many there are and their sum — a quick reference for factoring and number theory.Twin prime finderFind every pair of twin primes up to a limit — primes that differ by exactly 2, like (11, 13) or (17, 19). Enter an upper bound (up to 1,000,000) and it lists the pairs and counts them. Whether infinitely many exist is one of the oldest open problems in mathematics.Mersenne Prime CheckerRun the Lucas-Lehmer test on 2^p - 1 for any exponent p up to 5000, with the digit count, the rank in the known list and the even perfect number it generates.Prime Factor CalculatorFactor any integer up to 10^15 with Pollard's rho and Miller-Rabin, with the factor tree, exponent form, divisor count, sigma and Euler's totient.Amicable Number CheckerCheck whether two numbers are amicable — or give just one and get its candidate partner plus the verified loop, with perfect and sociable numbers identified.e Digits Calculator (Euler's Number)Compute up to 1,000 decimals of Euler's number e from the series Σ 1/k!, with digit frequencies, a digit search and the 1828 1828 trap explained.

Enter Number and the Prime number checker works out Prime?, Smallest divisor straight away. For instance, with Number = 97 it returns Prime? = yes and Smallest divisor = 97.

How to use it

  1. Enter your values: Number.
  2. Read the result instantly: Prime?, Smallest divisor.

Frequently asked questions

What does the Prime number checker actually compute?

It takes Number and derives Prime? and Smallest divisor from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

A single value: Number. Nothing else is required — no account, no file upload.

Can you show a worked example?

With Number = 97, the calculator returns Prime? = yes and Smallest divisor = 97. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

When would I actually use this?

Reading a number written another way: a Roman numeral on a monument, a hexadecimal colour, a binary byte, or a fraction that needs reducing.

What is the most common mistake?

Assuming a decimal fraction survives a change of base. A tenth is exact in decimal and infinitely repeating in binary, which is why 0.1 + 0.2 is not 0.3 in most programming languages.

What is the difference between the Prime number checker and the Prime factorization calculator?

This one returns Prime? and Smallest divisor; the Prime factorization calculator returns Prime factorization and Number of prime factors. That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

First n prime numbers is the closest one after this: List the first n prime numbers — the building blocks of arithmetic that have no divisors but 1 and themselves. Enter how many you want (up to 10,000) and it returns the sequence, the nth prime itself and the sum of them all.

What else is worth having open alongside it?

List of prime numbers and Twin prime finder — they come up in the same task often enough to be worth a second tab.

Where do the figures come from, and how current are they?

Base conversion and number-theory results are exact. Roman numerals follow the standard subtractive form used since the Middle Ages, which is not the only one the Romans themselves used.

Further reading

All guides →
How-toHow to Find Prime Factors: Factor Trees and the Division MethodBreak any whole number into its prime building blocks with a factor tree or repeated division — and write the result as a clean prime factorization with exponents.ExplainerSignificant Figures Explained: Counting, Rounding, and Why They MatterLearn what counts as a significant figure, the rules for leading, trailing, and captive zeros, and how sig figs keep your calculated answers honest.How-toHow to Multiply and Divide Fractions: Multiply Across, Flip to DivideMultiplying fractions needs no common denominator — just multiply across. Dividing means multiplying by the reciprocal. Learn both with worked examples and how to simplify.How-toHow to Round Numbers: Round Half Up, Round Half to Even, and MoreRound to any decimal place or number of significant figures, and learn when to use round half up versus round half to even to avoid bias.How-toHow to Add and Subtract Fractions: Common Denominator, Combine, SimplifyYou can only add or subtract fractions that share a denominator. Learn to find a common denominator, combine the numerators, and simplify the result, with a worked example.How-toHow to Do Long Division: Divide, Multiply, Subtract, Bring DownLong division breaks a big division into a repeating four-step cycle. Learn the divide-multiply-subtract-bring-down loop and how to read the remainder, with a worked example.
Prime number checker — OneKitly