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View Diary: Perhaps a simpler way to find out if a number is prime. (44 comments)

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  •  It's basically a variation on (5+ / 0-)

    the Sieve of Eratosthenes (SoE).

    Except - you don't indicate how your method already knows 5, 7, 11, 13, etc. are prime (without referring to a table of primes, I suppose). SoE figures that out on its own.

    It's never too late to have a happy childhood - Tom Robbins

    by badger on Mon Dec 05, 2011 at 01:12:10 PM PST

    •  Any number that ends in (0+ / 0-)

      .333 or .666 is prime before the number 25 which is a multiple of the first Prime after the number 3. That number is 5 the multiple of 5 is 25 and when divided by the number 3 ends in 8.333.
          We look at odd numbers that end in .333 or .666 starting from the number 1 and going to 25 for the reasons I just stated.
         We scratch off the multiples of primes whether multiplied by themselves or another prime we can find all prime numbers this way. I suspect we can find them this way simpler and faster without a computer. I would like a test of my idea vs other ideas mentioned in the comments on a computer.
           Until I get a chance to study the other ideas mentioned in the comments and I do mean STUDY so don't expect a reply until another diary.  And even then a computer test of speed is I admit  the ultimate test.
         Well all I can ask is does my idea work and am I right that after some time to study my idea does my idea work faster for humans than other methods to figure out if large groups of numbers starting from the number 1 are prime?
         I welcome challenges to prove my idea doesn't work and if it does not I will find an idea that does work.
          The Lefty Blogs are all about new ideas and proving them if I'm shown I'm wrong and my idea does not work at all then I will admit it.
          If there is a simpler way I will admit it. I am curious about how if my idea does work how it compares to computer ideas that do work.

      •  And how does your method know that (0+ / 0-)

        for example, 31 or 61 are primes, without being told? Either it doesn't, or you've left something out.

        Here's a hint: watch the animation at the wikipedia link above and think about how, once the program running the animation finds out that 11 is prime, it can fill in all the other primes on the chart with purple, without touching any other previously visited numbers - no multplying anything by 11 is necessary*, which is faster than the method you've described. It isn't necessary to test any of the "purple" primes in any way - the program already "knows" they're prime.

        *Except that 11 X 11 = 121

        It's never too late to have a happy childhood - Tom Robbins

        by badger on Mon Dec 05, 2011 at 04:48:03 PM PST

        [ Parent ]

        •  Did you try really try and understand (0+ / 0-)

          my idea? " for example, 31 or 61 are primes, without being told? Either it doesn't, or you've left something out."divide every odd number by the number  3 then since 5*5 the first prime after 3 is the first non prime number that ends in a .333 or .666 then every number that ends in a .333 or .666 is prime you multiple all the numbers that end in .333 or .666 by themselves and by the other numbers so yes 31 is prime because 7 the next prime number * 5 = 35 therefore 31 is prime. Just follow the steps. I will try and explain this better if I decide to do a next time. I am still studying your links.

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