Re: More on triangle numbers and primes!
- From: Dan <30pack@xxxxxxxxxxxxx>
- Date: Thu, 27 Oct 2005 10:36:34 EDT
>Well, let's do one...
>Is 31 prime ?
>31 \ 3 = 10
>9 \ 3 = 3
>10 - 3 = 7
>(7 * 3) + 9 = 30
>30 + 3 = 33
>There is not a 31 on row one...
>31 \ 4 = 7
>14 \ 4 = 3
>7 - 3 = 4
>(4 * 4) + 14 = 30
>30 + 4 = 34
>There is not a 31 on row two...
>31 \ 5 = 6
>20 \ 5 = 4
>6 - 4 = 2
>(2 * 5) + 20 = 30
>30 + 5 = 35
>There is not a 31 on row three...
>31 \ 6 = 5
>27 \ 6 = 4
>5 - 4 = 1
>(1 * 6) + 27 = 33
>There is not a 31 on row four...
>Row five begins with 35 which is greater than 33
>Finished.
>31 is prime
>Of course this out performs trial division when working >with larger numbers
>but not with small numbers...
Sure, that's how I found the 1,000 nth + prime.
You are just talking about stopping points here
because you had to go through the other primes >7
to get to prime 31. [11,13,17,19,23,29]
I knew the 1000 nth prime was >7000 but <8000 so
my last set I used was [8xxx,n] just to make sure
it was high enough for the check. Like your stopping
point [35,7] for your prime check 31.
Dan
.
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