Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫  π  -¹ ² ³ °

You are not logged in.

#1 2015-02-07 09:10:00

fireplace
Member
Registered: 2015-02-07
Posts: 1

What's everyone working on?

Myself trying find ways to use primes for other purpose than just cryptography.

So what are you guys working on?

Offline

#2 2015-06-15 22:24:18

Member
Registered: 2013-01-22
Posts: 131

Re: What's everyone working on?

I am working on finding a solution to proving whether a number is prime or not but at the moment I'm focusing on Goldbach's conjecture which states that any even number can be made up of two primes added together.

"Time not important. Only life important." - The Fifth Element 1997

Offline

#3 2015-06-15 22:43:29

zetafunc
Moderator
Registered: 2014-05-21
Posts: 2,109
Website

Re: What's everyone working on?

I am working on finding a solution to proving whether a number is prime or not

Like this?

Offline

#4 2015-06-16 02:03:51

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: What's everyone working on?

Working on a better way to determine the coefficients of large expansions. Only requires some research...

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Offline

#5 2015-06-17 03:31:03

Member
Registered: 2013-01-22
Posts: 131

Re: What's everyone working on?

zetafunc wrote:

Like this?

More like this;
x is not factorable by 2 or 5.
x = ab

x ends in 1; a and b end in (1,1)(3,7) or (9,9).
x ends in 3; a and b end in (1,3) or (7,9).
x ends in 7; a and b end in (1,7) or (3,9).
x ends in 9; a and b end in (1,9)(3,3) or (7,7).

i.e.  3x9=27.......ends in 7.
by knowing what x ends in we can determine what a and b might end in.

You would have thought knowing what a and b end in you could determine that a number is composite and therefore not prime, turns out it doesn't seem to work that way.

"Time not important. Only life important." - The Fifth Element 1997

Offline

#6 2015-06-17 07:01:33

zetafunc
Moderator
Registered: 2014-05-21
Posts: 2,109
Website

Re: What's everyone working on?

But is that really any better than, say, the Sieve of Eratosthenes?

You would have thought knowing what a and b end in you could determine that a number is composite and therefore not prime, turns out it doesn't seem to work that way.

It wouldn't -- using your notation, x is prime iff (a,b) = (1, x) or (x,1). Even if a or b is 1 modulo 10, that doesn't guarantee that a or b is 1, and for large x, will give you a very large number of possibilities.

Offline

#7 2015-06-17 07:58:49

Member
Registered: 2013-01-22
Posts: 131

Re: What's everyone working on?

zetafunc wrote:

Even if a or b is 1 modulo 10, that doesn't guarantee that a or b is 1, and for large x, will give you a very large number of possibilities.

If x = (10c + d)(10e + f) where d and f = 1,3,7 or 9 I just have to prove c and e > 0 granted that x is not factorable by 2,5,3,7. i.e. a and b > 10.

I know how to prove x is not factorable by 2,3,5 or 7, I don't know how to prove that c and e are both >0.

But say I knew what d and f were, you would have thought I'd be able to work out what c and e were................ Don't you think?

Last edited by Primenumbers (2015-06-17 22:46:30)

"Time not important. Only life important." - The Fifth Element 1997

Offline

#8 2015-06-19 00:00:48

Member
Registered: 2013-01-22
Posts: 131

Re: What's everyone working on?

Rule for primes;

x! is factorable by x only once when x is prime and more than once when x is not prime. This only happens when x>4.

If x=ab, ab occurs more than once, i.e. x!=axbxabx?

If x=

,
occurs more than once i.e. x!=ax2ax
. Unless
=2 or less and x= 4 or1. a>2 is fine.

I think this is simpler than x/x! factors down when x is not prime and doesn't when x is prime!

"Time not important. Only life important." - The Fifth Element 1997

Offline

#9 2015-06-23 10:21:21

Member
Registered: 2013-01-22
Posts: 131

Re: What's everyone working on?

zetafunc wrote:

But is that really any better than, say, the Sieve of Eratosthenes?

You would have thought knowing what a and b end in you could determine that a number is composite and therefore not prime, turns out it doesn't seem to work that way.

It wouldn't -- using your notation, x is prime iff (a,b) = (1, x) or (x,1). Even if a or b is 1 modulo 10, that doesn't guarantee that a or b is 1, and for large x, will give you a very large number of possibilities.

I still don't get this post..................? Is 1 modulo 10 a mathematical way of saying, ends in 1.....? I was trying to prove x is composite not prime......? a or b ending in 1 wouldn't guarantee x is prime...?

Last edited by Primenumbers (2015-06-23 10:28:57)

"Time not important. Only life important." - The Fifth Element 1997

Offline

#10 2015-06-23 11:17:15

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: What's everyone working on?

That is what

Even if a or b is 1 modulo 10

means. And of course zetafunc is correct ending in a 1 does not guarantee primality.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Offline

#11 2015-06-23 11:41:39

Member
Registered: 2013-01-22
Posts: 131

Re: What's everyone working on?

Ok, cool.

"Time not important. Only life important." - The Fifth Element 1997

Offline