Making this IsPrime function work. Please help!

[Geir]

I have just found this function that returns TRUE if a number in cell is prime number:

http://www.bluemoosetech.com/microso...rime%20Numbers

I am not getting this thing to work. I get a #NAME? error when using it.

What are the proper steps to implement this function?!

[Roger Govier]

Hi

It sounds as though you haven't copied the code supplied into a standrad module in the VB Editor.

Copy the Code in the example
Alt+F11 to invoke the VB Editor
Insert>Module
Paste code into white pane that appears
Alt+F11 to return to Excel

To use
With any number in say, cell A1, enter in B1
=ISPRIME(A1)

[shg]

That function will take a loooooong time to check a large number, and it only accommodates numbers to the size of a Long. Try this one (same instructions as Roger suggested, but you can't have both in the same workbook, since they have the same name).

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If you want the first factor instead of False when the number is not prime, set the optional second argument TRUE.

[Roger Govier]

Hi

i hadn't bothered to take a look at the actual code, merely tried to point you in the direction of entering what you had in the correct place.

If you want an efficient function for doing this, then the following (produced by the late George Simms) is the best that I have seen.

As mentioned by shg, you can't have this in the same module unless you rename the other functions first.

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[shg]

That is indeed better, but still limited to a Long.

And why need the function be volatile?

[Geir]

I tried using the code and instructions you provided but I still get a #NAME? when entering the =IsPrime(C6) inside a cell.

The excel file is xlsm type

Maybe there is some excel config. option that needs to be enabled?!

[shg]

Nope, that's all you need to do.

Please post the workbook as you have attempted it.

[Geir]

I made it work but not in the original file. For some or other reason it does not run there.

Would anyone please tell me how to make it return "1" or "One" when it considers a cell with the number 1 inside?!

Thanks for all the help at this great forum!

[shg]

=if(a1=1, 1, isprime(a1))