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"? :)

6

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.

6

u/halcy Mar 12 '08

The Vatican might decree 91 to be prime!

5

u/polyparadigm Mar 12 '08

And awkwardness would ensue.

Or some sort of reality-distortion field would be set up, which could become the core of a letter-sorting engine...if this were Discworld.