shmoe said:
1. Ahh, I see. This could be a function of looking at only small numbers where the distances between two primes is even smaller, and an unnaturally large percentage of "small" odd numbers are prime. Up to the first 100 or so primes the largest gap is 17 numbers long. If all these gaps were somehow randomly chosen odd numbers from 1 to 17, you'd expect about 6/9 of them to be prime, which turns out to be close to the truth.
I ran my program from about 1,000,973 to 1,002,361 and came up with these results:
7, 17, 3, 13, 5, 3, 13,
27, 11, 5, 1, 3, 13,
15, 29, 5, 13, 3, 13, 5,
21, 17, 29, 11, 11, 11, 7,
9, 1, 3, 19, 5,
15, 11, 5, 1, 11,
9, 19,
15, 11, 7, 23,
9,
25, 3, 17, 1, 11, 5, 17, 5,
27, 7,
9, 19,
9, 13, 3,
25,
9, 19,
39, 13, 3, 5, 1, 11,
9, 7, 71,
21, 7, 5, 5, 23, 3, 1, 5,
27, 31, 11, 11, 3, 5, 7,
9, 7, 11,
21, 5, 1,
21, 17,
35, 13, 5,
9, 1, 3,
25,
9, 41, 1, 3, 1,
9, 1,
15
The ratio here is presicely 27/109 (or about 1/4). Less than 2/3; but fairly close. Interesting that the ones that most come up which are not prime numbers are divisible by prime numbers... some big endless loop I'm sure, since you take those (ie. 9, 15, 21, 27) and we find that they are divisible by three and some other prime number... and it continues... I don't dare push my program too far. It already takes almost 0.10 seconds to calculate terms over 5,000,000. I did it in C++ if anyone wants the code (it's pretty small).
EDIT: Another quick note. The amount of numbers listed here always seems to be divisible by a prime number. Do they take that into account when they attempt to find a prime?
ADDITIONAL EDIT: They are divisible by any prime that I can calculate, except for the number 2 (of course), so I would submit that 2 is not in the same category... not that it couldn't still be a prime; but it's not the same type.
shmoe said:
2. If a test declares a number prime, why would you want to apply another primality test to it? There are some "probabilistic" primality tests where you do repeated applications, but I don't think that's what you meant. Google "primality testing", you'll probably find heaps of info.
I did mean "probabilistic" there. You're right, it wouldn't make much sense using another prime number test on a prime number.
shmoe said:
3. It's probably not coincidental. There are convincing heuristic arguments (read-arguments with gaps in them) that would indicate there are infinitely many prime pairs. It is also known that there are infinitely many pairs p, p+2 where one is prime and the other has at most 2 prime factors, that's coming tantalizingly close to a solution (yet so far out reach still).
Wow! Sounds like they're on the right track. I'm not great with number crunching. I just do the thinking.
shmoe said:
Next best thing to primes would be a low number of prime factors. In some ways they can be hard to separate (see paragraph above). Prime powers are also pretty decent too.
Interesting. I wouldn't have thought of prime powers.
shmoe said:
not sure what you mean about "infinite is not a concept that would match a prime number sequence", since you seem to agree there is no largest prime and therefore infinitely many of them.
I'm not sure either... I guess what I was getting at was that since infinity isn't really a defined quantity; but a concept, or limit, or... help me out here... anyway... since it's not a "natural number" (I think that's what you've called it), then saying that numbers (which happen to be "natural numbers") have an infinite limit (limit that is not "natural") seems to conflict. Though I'm sure it doesn't but it sounds like it.
shmoe said:
4. Quite the opposite about the sum of recipricals of the primes diverging, showing this sum diverges is one way to prove there are infinitely many of them. If there were a finite amount, then this sum would have a finite value. However by adding up enough terms, you can make this sum as large as you like. It turns out if you add up 1/p for all primes less than say x, you'll get about log(log(x)), which although going to infinity very slowly, it still goes.
Interesting as well... I must have missed something in my math classes. I, for some reason, am not aware of the relationship between primes and log(x); but many people seem to have mentioned it. What is that relationship exactly?