On Nov 16, 2005, at 11:53 AM, Peter wrote:

>
>>>>  (Only the same 8 numbers within any given 30 sequentially numbered
>>>>  group are potentially prime).
>>
>>> Except for 0 to 30, which has 10 or 11 primes (depending on how you
>>> feel about "1") ?  Even without 2, there are still more than 8 
>>> primes.
>>
>> Error 314159:   Invalid range specified    Range 0 - 30 contains more 
>> than 30 numbers.


Ok. Since the algorithm acts on (N*30)+..., I guess we're talking about
the range 0 to 29 for N=0.  It's still got more than 8 odd primes (3, 5,
7, 11, 13, 17, 19, 23, 29) plus 2, of course...  Looks like the trouble
makers are 2, 3 and 5; the algorithm says "(N*30) has those factors for
all N and therefore can't be prime, but the N=0 case is special cause
it's the ONLY factor...

In my own "find the prime numbers" program, I didn't bother remembering
the non-prime numbers; I just tested all the odd numbers against the
list of primes I already had.  I wonder where the break-even point in
storage is...

It was a very educational experience,  The main thing I learned was
that actually outputting the primes was MUCH more expensive than
merely calculating them and leaving them in memory.  (IIRC, I only
calculated the first 100k primes.)  I wonder where the break-even
point for THAT was.  thousands of instructions to do that IO system 
call,
vs 1  (none, really) to leave the prime sitting in memory...

BillW
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