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

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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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3 Responses to “Filter one table if the value is in another table (Formula Trick)”

  1. Montu says:

    What about the opposite? I want a list of products without sales or customers with no orders. So I would exclude the ones that are on the other table.

    • Chandoo says:

      Good question. You can check for the =0 as countifs result. for example,
      =FILTER(orders, COUNTIFS(products, orders[Product])=0)
      should work in this case.

      PS: I have added this example to the article now.

  2. Raphael says:

    Hi there!

    Could i check if there was a way to return certain fields of the table only?

    so based off your example above, i would like to continue to use the 'Products" table as a way to filter out items from my "Orders" table, but only want to show maybe only the "Product" and "Order Value" fields, rather than all 5 fields (sales person, customer, product, date, order value).

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