• palordrolap@fedia.io
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    5 days ago

    Felt like noodling a little with some numbers. I have a nice candidate. 22301. Pretty small, right? It’s prime. That’s not troubling to most anyone’s sanity. Edit: one should check one’s silly code more carefully before madly pretending to be mad on the Internet. It is not prime. But the intermediate numbers still are.

    There’s something that can be done to that number four times (but no more) which results in a prime each time and the fourth step results in a 70 digit number that I may have looked at slightly tOo LoNnNg.

    Edit 2: Attempt at redemption for the math if not the joke: Start with 5497949 which is prime, and you can do the thing four times and get a prime each time. The last one has 108 digits and, no word of a lie, starts 6969…

    Imaginary bonus points for guessing what the heck the operation / something is.b

    • jaupsinluggies@feddit.uk
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      4 days ago

      If you divide it by itself and add one, you can do that infinitely many times and get a prime every time. Works for all the primes.

      • sga@piefed.social
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        3 days ago

        it also works for all perfect numbers (by definition non prime), and also triangle numbers (all triangle numbers greater than 3 or non prime), and also for all numbers above 42, and below 69. quite a neat property sir.