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submitted 9 months ago by [email protected] to c/[email protected]
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[-] [email protected] 30 points 9 months ago

Some superstitious nerdy teenagers convinced small child me that 91 was a universal anomaly bc it’s 13 (bad luck) * 7 (good luck), so my weird brain never saw 91 as prime , & I can’t be the only person this happened to

[-] [email protected] 22 points 9 months ago
[-] [email protected] 32 points 9 months ago

Naw, 5 + 1 = 6, 6 is divisible by 3, so 51 is divisible by 3.

[-] [email protected] 4 points 9 months ago

I shared this at work recently and nobody cared. 3 6 and 9 are all kinda special.

[-] [email protected] 19 points 9 months ago* (last edited 9 months ago)

Only if you weren't taught (or were, but too long ago lol) the divisible by 3 rule - if the sum of the digits is divisible by 3, so is the whole number. 5+1=6 therefore 51 is divisible by 3! Bonus division rule - if it was also an even number and therefore divisible by 2, you could deduce that the whole number was divisible by 6.

[-] [email protected] 26 points 9 months ago
[-] [email protected] 4 points 9 months ago

Actually, 51 is not divisible by 3!

It is divisible by 3

[-] [email protected] 1 points 9 months ago
[-] [email protected] 4 points 9 months ago

Surely it's 1? Looks prime, and some people will even argue that it is!

[-] [email protected] 4 points 9 months ago

Its only factors are 1 and itself after all

[-] [email protected] 3 points 9 months ago

Agreed. 51 looks prime AF.

[-] [email protected] 6 points 9 months ago

I always felt that 21 should be, but nooo. Stupid 7

[-] [email protected] 5 points 9 months ago* (last edited 9 months ago)

21 should be

2 + 1 = 3, therefore 21 is divisible by 3 and is not prime. QED :)

[-] [email protected] -1 points 9 months ago

9+1 = 10, therefore 91 is divisible by 10 and is not a prime ... QED, I guess

[-] [email protected] 3 points 9 months ago

In the right base, that might work.

[-] [email protected] 2 points 9 months ago

It's funny, but actually a good proof

this post was submitted on 22 Sep 2024
109 points (97.4% liked)

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