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

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

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