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threelonmusketeers@sh.itjust.works to Math Memes@lemmy.blahaj.zoneEnglish · 8 months ago

John Conway proves that 91 is the smallest number which looks prime but isn't

www.youtube.com

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John Conway proves that 91 is the smallest number which looks prime but isn't

www.youtube.com

threelonmusketeers@sh.itjust.works to Math Memes@lemmy.blahaj.zoneEnglish · 8 months ago
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  • I'll be on ShareMySims@lemmy.dbzer0.com@sh.itjust.works
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    8 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.

    • Xtallll@lemmy.blahaj.zone
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      8 months ago

      Actually 51/3! Is 8.5

      • Cadeillac@lemmy.world
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        8 months ago

        You bastard

      • threelonmusketeers@sh.itjust.worksOP
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        8 months ago

        !unexpectedfactorial@sopuli.xyz

    • Nougat@fedia.io
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      8 months ago

      Actually, 51 is not divisible by 3!

      It is divisible by 3

      • I'll be on ShareMySims@lemmy.dbzer0.com@sh.itjust.works
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        8 months ago

        Hilarious.

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