Prime Number Checker to Check if Numbers are Primes

Prime Number Checker Calculator Sign

This calculator will let you know whether or not a given number is a prime (natural) number -- with the click of a button.

Plus if it turns out the entry is not a natural number, the calculator will report the first divisor it found, as well as show the equation and the quotient.

If you would like to find all primes for a given composite, please visit the Prime Factorization Calculator.

Or, if you wish to generate a customizable, printable list of primes, please visit the Primes List Generator.

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Prime Number Checker Calculator

Check to see if a number is prime, and if it's not, see the first divisor found.

Special Instructions

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Selected Data Record:

A Data Record is a set of calculator entries that are stored in your web browser's Local Storage. If a Data Record is currently selected in the "Data" tab, this line will list the name you gave to that data record. If no data record is selected, or you have no entries stored for this calculator, the line will display "None".

DataData recordData recordSelected data record: None
# to check:Number to check:Number to check if prime:Number to check if prime:

Number to check if prime:

Enter a number that is greater than 1 that you want to perform a prime check on. Numbers greater than 1 million may cause the prime number checker to time out before it completes its calculations.

Prime?Is number prime?Is the entered number a prime number?Is the entered number a prime (natural) number?

Is the entered number a prime (natural) number?

This will be a yes or no result. Yes indicates the entered number is prime, and No indicates the entered number is not prime. If the answer is No the prime number checker will report the first divisor it found.

If you would like to save the current entries to the secure online database, tap or click on the Data tab, select "New Data Record", give the data record a name, then tap or click the Save button. To save changes to previously saved entries, simply tap the Save button. Please select and "Clear" any data records you no longer need.

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Help and Tools


What prime numbers are.

What Are Primes?

Primes, or natural numbers are any numbers that are greater than 1 that are only divisible by 1 and the numbers themselves.

For example, 13 is a natural number because nothing other than 1 and itself can be divided evenly into 13.

The integer 14, on the other hand, is not a natural because it can be divided evenly by the factors 1, 2, 7, and 14 (see the Factoring Calculator to quickly find all factors of a number).

The integer 14 and other non-primes are also referred to as composite numbers.

Adjust Calculator Width:

Move the slider to left and right to adjust the calculator width. Note that the Help and Tools panel will be hidden when the calculator is too wide to fit both on the screen. Moving the slider to the left will bring the instructions and tools panel back into view.

Also note that some calculators will reformat to accommodate the screen size as you make the calculator wider or narrower. If the calculator is narrow, columns of entry rows will be converted to a vertical entry form, whereas a wider calculator will display columns of entry rows, and the entry fields will be smaller in size ... since they will not need to be "thumb friendly".

Show/Hide Popup Keypads:

Select Show or Hide to show or hide the popup keypad icons located next to numeric entry fields. These are generally only needed for mobile devices that don't have decimal points in their numeric keypads. So if you are on a desktop, you may find the calculator to be more user-friendly and less cluttered without them.

Stick/Unstick Tools:

Select Stick or Unstick to stick or unstick the help and tools panel. Selecting "Stick" will keep the panel in view while scrolling the calculator vertically. If you find that annoying, select "Unstick" to keep the panel in a stationary position.

If the tools panel becomes "Unstuck" on its own, try clicking "Unstick" and then "Stick" to re-stick the panel.