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## How to check if the number is prime number in Excel?

As we all known, a prime number is a natural number which contains only two distinct natural number divisors: One and itself. If you have a list of numbers in a worksheet, how could you check if the numbers are prime numbers?

Check if a number is prime number with array formula

Check if a number is prime number with User Defined Function

#### Check if a number is prime number with array formula

The following formula can help you identify the number whether it is a prime number or not, please do as this:

1. Enter the following formula into a blank cell – C2 for example beside your data:

=IF(A2=2,"Prime",IF(AND(MOD(A2,ROW(INDIRECT("2:"&ROUNDUP(SQRT(A2),0))))<>0),"Prime","Not Prime")) (A2 is the cell contains the number that you want to check), and then press Ctrl + Shift + Enter keys together, and you will get the result, if the number is prime, it will display “Prime” in the cell, if not, “Not Prime” will be displayed, see screenshot: 2. Then select the cell C2, and drag the fill handle down to the cells which you want to apply this formula, and all the numbers will be identified if is prime number or not. See screenshot: #### Check if a number is prime number with User Defined Function

The following User Defined Function also can help you to check the numbers if prime or not, please do as follows:

1. Hold down the ALT + F11 keys to open the Microsoft Visual Basic for Applications window.

2. Click Insert > Module, and paste the following code in the Module Window.

VBA code: Check if a number is prime or not:

``````Function CheckPrime(Numb As Single) As Boolean
'Updateby Extendoffice
Dim X As Long
If Numb < 2 Or (Numb <> 2 And Numb Mod 2 = 0) _
Or Numb <> Int(Numb) Then Exit Function
For X = 3 To Sqr(Numb) Step 2
If Numb Mod X = 0 Then Exit Function
Next
CheckPrime = True
End Function
``````

3. Then save and close this code, go back to the worksheet, and enter this formula: =checkprime(A2) into a blank cell beside your number list, and then drag the fill handle down to the cells which you want to contain this formula, if the number is prime number, it will display TRUE, if not, it will display FALSE, see screenshot: ### The Best Office Productivity Tools

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This comment was minimized by the moderator on the site
Hi there, I like your article. Thanks a lot. My simple tests showed that 99 was a prime number while 99 is not as 99 is divided by 3 and 33 as well as 1 and 99. Can you let me know what is wrong with my operation?
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The array formula above doesn't work but the User Defined function does and was very helpful.Thanks!
This comment was minimized by the moderator on the site
The array formula doesn't work but the User defined function does and was very helpful. Thanks!
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The user defined function does not seem to work for numbers above ~16777213
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this is my fastest version Sub generateprimenumbersbetween3() starting_number = 1 'input value here last_number = 30000 'input value here primenumbers = "" For a = starting_number To last_number c = a For b = 2 To c If a Mod b = 0 And c b Then Exit For Else If b = c Then primenumbers = primenumbers & " " & a Exit For Else If Round(a / (b + 1)) + 1 > b Then c = Round(a / (b + 1)) + 1 End If End If End If Next b Next a MsgBox primenumbers End Sub Sub ISPRIME3() number_to_be_checked = 2000000000 'input value here c = number_to_be_checked For b = 2 To c If number_to_be_checked Mod b = 0 And c b Then MsgBox "Not Prime. Divisible by " & b Exit Sub Else If b = c Then MsgBox "Prime" Exit Sub Else If Round(number_to_be_checked / (b + 1)) + 1 > b Then c = Round(number_to_be_checked / (b + 1)) + 1 End If End If End If Next b End Sub
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Your formula is not working. Eg. 1681 is NOT a prime but by formula it is.
=IF(A2=2,"Prime",IF(AND(MOD(A2,ROW(INDIRECT("2:"&ROUNDUP(SQRT(A2),0))))<>0),"Prime","Not Prime"))
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Hello, Jan,
The above formula is correct, after pastingt the formula into a cell, you should press Ctrl + Shift + Enter keys together, not just Enter key.
Please try it again, thank you!
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Yes, it was that case with CSE. Thanks (it's fixed now).
https://superuser.com/questions/674566/when-to-use-ctrlshiftenter-and-when-to-use-enter-in-excel

Btw Czech variant to:
=IF(A2=2,"Prime",IF(AND(MOD(A2,ROW(INDIRECT("2:"&ROUNDUP(SQRT(A2),0))))<>0),"Prime","Not Prime"))
is:
=KDYŽ(A2=2;"Prime";KDYŽ(A(MOD(A2;ŘÁDEK(NEPŘÍMÝ.ODKAZ("2:"&ROUNDUP(ODMOCNINA(A2);0))))<>0);"Prime";"Not Prime"))

Compare: https://imgur.com/a/4MgeV
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well 4095 is not a prime. still it gives result as prime no though. its incorrect.
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Hello, vaibhav,
When you pasting above formula, you should press Ctrl + Shift + Enter keys together, not just Enter key, please try it again.
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There's a reference error when you type in numbers that have more than 12 digits.
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Hello,Nathan,
As you said, when the numbers are longer than 12 digits, it will become scientific notation. The formula is not applied for this formatting.
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Yes it worked wen I did Ctrl+Shift+Enter... !! Thank you..:D and Do u mind explaining the algorithm please.
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Hi.

I am using an italian version of Excel, so the formula does not work and i have an error. Can you help me?

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Hi, Gian,
If the formula does not work correctly for you, you can apply the second method-User Defined Function. Please try, hope it can help you!
Thank you!
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Hi skyyang.
If it can be useful for others researchers, I inform you that I have found the solution to my problem here => http://www.riolab.org/index.php?option=com_content&view=article&id=172&Itemid=68

Thank you!
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There is definitely a problem with this equation. I did a direct copy/paste and checked it was a faithful copy but it still has 9, 15, 21, 25, 33, 35 and 39 as primes when they obviously are not. On quick inspection it seems as if factors of 3 and 5 are giving rise to some sort of problem. It is a very complicated formula for a single cell - so much so, I can't work out what it is trying to do. I usually break such things down into multiple cells to make debugging easier (which, I believe is Excel best practice).
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There is definitely a problem with this equation. I did a direct copy/paste and checked it was a faithful copy but it still has 9, 15, 21, 25, 33, 35 and 39 as primes when they obviously are not. On quick inspection it seems as if factors of 3 and 5 are giving rise to some sort of problem. It is a very complicated formula for a single cell - so much so, I can't work out what it is trying to do. I usually break such things down into multiple cells to make debugging easier (which, I believe is Excel best practice). The function seems to work, though.
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DO NOT ENTER THE FORMULAE IN THE CELL. Select the cell then paste the formulae in the formulae bar and press ctrl+shft+Enter. it should put { around the formulae} otherwise its wrong.
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Craig, Thanks - that works! Sorry, I didn't read the instructions sufficiently carefully.
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