Prime number + 2 = Prime number
06-24-2016, 07:53 PM (This post was last modified: 06-24-2016 08:15 PM by Ivan Rancati.)
Post: #1
 Ivan Rancati Junior Member Posts: 8 Joined: Mar 2014
Prime number + 2 = Prime number
EDIT: oops. Twin primes, plenty of study on that already. Sorry for the old news

I read this riddle in a 1950s encyclopedia (in Italian), and it piqued my interest.

Adding some prime numbers to 2 still yields a prime number
For example
3, 5
5, 7
11, 13
17, 19
41, 43
and so on

How could one possibly go about proving that there is an infinite number of these "prime pairs", or that past a certain prime number there is never going to be such a pair?

cheers
Ivan
06-24-2016, 08:17 PM (This post was last modified: 06-24-2016 08:19 PM by Ron Ross.)
Post: #2
 Ron Ross Junior Member Posts: 47 Joined: Mar 2014
RE: Prime number + 2 = Prime number
I was going to suggest looking at Mersenne prime numbers, as they can be used to help find these pair of primes separated by 2.
.
06-24-2016, 09:52 PM (This post was last modified: 06-24-2016 10:52 PM by Vtile.)
Post: #3
 Vtile Senior Member Posts: 404 Joined: Oct 2015
RE: Prime number + 2 = Prime number
(Any integer above number 2) = 2 * A + 3 * B (in my mind)

5 = 2 * 1 + 3 * 1
7 = 2 * 2 + 3 * 1
8 = 2 * 4 + 3 * 0
9 = 2 * 0 + 3 * 3
10 = 2 * 2 + 3 * 2
11 = 2 * 4 + 3 * 1
12 = 2 * 6 + 3 * 0
13 = 2 * 2 + 3 * 3
14 = 2 * 7 + 3 * 0
15 = 2 * 6 + 3 * 1
16 = 2 * 2 + 3 * 4
17 = 2 * 7 + 3 * 2
18 = 2 * 6 + 3 * 2
19 = 2 * 8 + 3 * 1
...
41 = 2 * 19 + 3 * 1
43 = 2 * 19 + 3 * 3
as seen there is plenty of possibilities that that prime + 2 is prime...

Soo there is also prime + 4 = primes (37, 41) and prime + 3 = prime(s?) (2, 5) and prime + 6 = primes etc..

In that light this weren't a suprise for me, although I see it as interesting pattern
that I'm not interested to search, but like..
Code:
  1   ? 0?  2 , 1   3,  1  5,  2  7,  2  11, 4   13, 2   17, 4   19, 2  23, 4  29, 6 <- 1st 6 = 2*3 or 2^2 + 3^0 or 2^2 + 2^0  31, 2  37, 6  41, 4  43, 2  47, 4  53, 6  59, 6  61, 2  67, 6  71, 4  73  2

So 1001 can be written in as 500d, 1b as 2*500 + 2^0 or something like 250d,11b yeah, I'm inventing as writing so this makes no sense per se so time to go to sleep.
edit2 typo 2^1 -> 2^0
06-24-2016, 11:26 PM
Post: #4
 John R Member Posts: 101 Joined: Dec 2013
RE: Prime number + 2 = Prime number
(06-24-2016 07:53 PM)Ivan Rancati Wrote:  How could one possibly go about proving that there is an infinite number of these "prime pairs", or that past a certain prime number there is never going to be such a pair?

There have been some recent developments in this regard.

John
06-25-2016, 12:52 AM
Post: #5
 Vtile Senior Member Posts: 404 Joined: Oct 2015
RE: Prime number + 2 = Prime number
Thx for the OP for this thread, made me 1st time (since educational math is as interesting as wet socks ) to think about nature of the complementary things in maths.
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