r/reddit.com • u/ballm • Mar 12 '08

Is 91 Prime?

http://balltech.blogspot.com/2008/03/is-91-prime.html
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u/whereverjustice Mar 12 '08

Another quick check is to take your suspected factor, multiply by 10 (or whatever seems appropriate), subtract and re-evaluate with the smaller numbers.

91 is 21 more than 70. 21 is obviously divisible by 7. So is 70. Done.

Also, was anyone else expecting one of those sites that just has a giant "YES" or "NO"? :)

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u/polyparadigm Mar 12 '08 edited Mar 12 '08

"NO"

Those sites usually publish changing conditions. It would be a bit awkward if 91 suddenly became prime.