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Array formula to check if a number is prime [just for fun]

  • Last updated on May 29, 2009
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Chandoo

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I am math-geek-wannabe, if there ever is such a category. During my 3rd year of graduation I went and purchased the volume 2 of Donald Knuth‘s Art of Computer Programming and thus began my love with all things random and prime. I never really became the math-geek I always wanted to, instead I became an insurance expert with tons of passion for data and visualization. But when I get a chance to poke with randomness or numbers, I always lap it up with joy. And that brings us to an interesting array formula trick to check if a number is prime or not.

(assuming the number is in the cell B5) type the below formula and

=IF(MIN(MOD($B$5,ROW(INDIRECT("2:"&INT(SQRT($B$5))))))=0,"not prime","prime")

hit ctrl+shift+enter and bingo, it tells you if the number is prime or not.

how it works?

take a guess…

you are right. It just calculates the minimum of all reminders when the number x is divided by values between 2 and sqrt(x) and sees if it is zero. If so, the number is “not prime”, else, it is a “prime number”.

More random stuff on randomness and numbers

Shuffle a list of values in excel using random numbers

Bingo / Housie Tickets in Excel

Correct way to simulate dice throws in excel

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One Response to “How to compare two Excel sheets using VLOOKUP? [FREE Template]”

  1. Danny says:
    September 4, 2024 at 10:59 am

    Maybe I missed it, but this method doesn't include data from James that isn't contained in Sara's data.

    I added a new sheet, and named the ranges for Sara and James.

    Maybe something like:
    B2: =SORT(UNIQUE(VSTACK(SaraCust, JamesCust)))
    C2: =XLOOKUP(B2#,SaraCust,SaraPaid,"Missing")
    D2: =XLOOKUP(B2#,JamesCust, JamesPaid,"Missing")
    E2: =IF(ISERROR(C2#+D2#),"Missing",IF(C2#=D2#,"Yes","No"))

    Then we can still do similar conditional formatting. But this will pull in data missing from Sara's sheet as well.

    Reply

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