Sorry, an error occurred while loading the content.

## [PrimeNumbers] Twin primes Criteria (Correction)

Expand Messages
• Hi Flavio As Paul Jobling pointed out, your conjecture is equivalent to the criteria (2) and (3) below. A more thorough investigation shows that both these
Message 1 of 1 , Mar 29, 2001
Hi Flavio

As Paul Jobling pointed out, your conjecture is equivalent to
the criteria (2) and (3) below. A more thorough investigation
shows that both these equivalent versions are indeed correct.

Mike Oakes appears to be mistaken or I am missing something?

I base this on the following Mathematica snippet:

Do[p=Prime[i];
If[Mod[p,4]==1, r=-1, r=+1];
If[PrimeQ[p]&&PrimeQ[p+2],
m=Mod[2((p-1)/2)!^2 - r(5*p+2),p(p+2)];
If[m!=0,Print["False"];
];
];
,{i,2,PrimePi[10^4]}];

In 1949 using Wilson's Theorem* P. A. Clement published
a proof that p and p+2 are both prime ("twin primes")
if and only if the following congruence holds:

(1) 4((p-1)! + 1) + p = 0 [mod p(p+2)]

Furthermore in 1995 Joseph B. Dence & Thomas P. Dence
reduced the Clement criterion to the following two criteria:

(2) 2((((p-1)/2)!)^2 + 1) + 5p = 0 [mod p(p+2)]
if and only if p and p+2 are primes and p=4k+1

(3) 2((((p-1)/2)!)^2 - 1) - 5p = 0 [mod p(p+2)]
if and only if p and p+2 are primes and p=4k-1

A similar criterion exists for the primality of p and p+d:

If p>1 and d>1 are both integers, then p and p+d are both
prime if and only if:

( 1 ((-1)^d)d! ) 1 1
(4) (p-1)! ( - + ---------- ) + - + --- is an integer
( p p+d ) p p+d

In addition P. A. Clement's paper proves similar necessary and
sufficient criteria for prime triples p, p+2 and p+6 as well
as prime quadruplets p, p+2, p+6, p+8. If these are of general
interest I can post them to the list.

Regards

Alan Powell

* Wilson's Theorem:
An integer p>1 is prime if and only if (p-1)! + 1 = 0 [mod p]

At 09:06 AM 3/27/01, torasso.flavio@... wrote:

> I found the following rule concerning twin primes:
> n and n+2 are both prime iff
> 2 [(n-1)/2]!^2 = \pm (5n+2) mod n(n+2)
> the sign being "+" when n=4k-1, "-" when n=4k+1.
>
> Is it an interesting or trivial result?
> Are there similar congruences for other prime pairs?
>
> Thanks for any comments
Your message has been successfully submitted and would be delivered to recipients shortly.