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It looks so wrong (sh.itjust.works)
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[-] elvith@feddit.org 22 points 1 week ago

The digit sum of 51 is 6, which is divisible by three. So 51 is also divisible by three. It’s not even hard to see that it’s not prime.

[-] sugar_in_your_tea@sh.itjust.works 15 points 1 week ago* (last edited 6 days ago)

Yup, my personal prime check is:

  1. Even?
  2. Ends in 5?
  3. Digits sum to 3?

If it fails all three and it's not an "obvious" prime (<20), then it's prime enough for me.

Also

Ends in 0,

but that's covered by 5 really.

It's also covered by being even.

this post was submitted on 11 Dec 2024
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