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## #1 2013-04-26 18:56:39

mathaholic
Member
From: Earth
Registered: 2012-11-29
Posts: 3,247

### Sexy primes

Sexy primes are two prime numbers, wherein their difference is 6. I got this from a video on YouTube : http://www.youtube.com/watch?v=WJ12DYBuazY

Now, examples of sexy primes :
5 and 11
11 and 17
...

Sexy triplets :
5 11 17
11 17 23
...

5 11 17 23
11 17 23 29

Sexy quintuplets :
5 11 17 23 29

There are no sexy primes that are groups of 6. That's it! Discuss about it!

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## #2 2013-04-26 23:47:15

Agnishom
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From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,442
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### Re: Sexy primes

I got this from wolfram mathworld.
I don't think they are much sexy...

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.

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## #3 2013-04-27 16:44:43

mathaholic
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From: Earth
Registered: 2012-11-29
Posts: 3,247

### Re: Sexy primes

I saw it from YouTube, because pf six, that sound like "gender". That's why they're called sexy primes. )

Mathaholic | 10th most active poster | Maker of the 350,000th post | Person | rrr's classmate

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## #4 2013-04-27 21:32:42

Agnishom
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From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,442
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### Re: Sexy primes

Yeah I know..

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.

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## #5 2013-04-28 00:13:50

mathaholic
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From: Earth
Registered: 2012-11-29
Posts: 3,247

### Re: Sexy primes

Oh. No abs, right?

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## #6 2013-04-28 01:22:33

Agnishom
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From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,442
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### Re: Sexy primes

Is 6 the smallest possible common difference in AP of more than three primes?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.

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## #7 2013-04-28 06:29:25

Nehushtan
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Registered: 2013-03-09
Posts: 882
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### Re: Sexy primes

Agnishom wrote:

Is 6 the smallest possible common difference in AP of more than three primes?

Is such a sequence possible?

Last edited by Nehushtan (2013-04-28 06:30:51)

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## #8 2013-04-28 08:18:11

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 107,190

### Re: Sexy primes

There are many with a common difference of 6, but none smaller.

Proof is easy.

Hint: Combinatorics is the model! Step out of the box or maybe jump into it.

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.

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## #9 2013-04-29 00:59:10

anonimnystefy
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From: Harlan's World
Registered: 2011-05-23
Posts: 16,018

### Re: Sexy primes

Well, first note that the common difference must be an even number, and if it is less than 6, then it must be either 2 or 4. Also notice that if two numbers differ by 2, 4 or 8, they have different remainders modulo 3. This means that in three numbers in an AP with common difference 2 or 4, one will surely be divisible by 3. It is now easily proved that an AP of 4 or more terms and common difference 2 or 4 cannot exist.

There are only two AP's of 3 terms and those are 3, 5, 7 and 3, 7, 11.

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #10 2013-04-29 12:46:09

Agnishom
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From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,442
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### Re: Sexy primes

Thanks for the proof

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.

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## #11 2013-04-29 12:47:47

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 107,190

### Re: Sexy primes

There is one that I came up with that is quite simple.

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.

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## #12 2013-04-29 12:51:59

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,018

### Re: Sexy primes

And that is?

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #13 2013-04-29 12:53:03

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 107,190

### Re: Sexy primes

Boxes and dashes like in combinatorics!

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.

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## #14 2013-04-29 13:01:07

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,442
Website

### Re: Sexy primes

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.

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## #15 2013-04-29 13:11:39

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 107,190

### Re: Sexy primes

We can view the number line in terms of boxes and dashes. The boxes are multiples of three, the dashes are the two numbers between each multiple of 3 that is greater than 3.

WLOG we can presume the lowest prime is located at position1 or position2. See the diagram. If we start at positon1 and count off 2 from it we see in the top drawing that not even a prime pair is possible from this position.

If we start from position2 and count off by 2 we see that a prime triplet with constant difference of two is also impossible

If there is no possible prime triplet with difference of two ( after 3, 5 and 7 )there is obviously no quadraplets, quintuplets etc. That concludes the proof.

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.

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## #16 2013-04-29 13:14:36

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,018

### Re: Sexy primes

That is the same as my proof.

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #17 2013-04-29 13:16:15

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 107,190

### Re: Sexy primes

But it does not require any mathematical jargon or concepts other than counting.

Proof that there is no triplet with common difference 4.

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.

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## #18 2013-04-29 13:20:50

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,018

### Re: Sexy primes

It is the same proof worded differently.

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #19 2013-04-29 13:23:50

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 107,190

### Re: Sexy primes

Hi anonimnystefy;

I did not offer it as a superior proof. I said it was a different one. Someone, like me for instance can understand this one a little easier. This is almost a proof without words.

Also, it is not the same proof. Yours uses words like modulo and AP. This one does not need to.

I think it also solves harder problems easier.

For instance: if I asked whether there were any 7 tuplets with a difference of 2,4,4,4,4,2, I can answer that very quickly by drawing more boxes and more dashes. No math required. Answer is no!

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.

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## #20 2013-04-29 13:54:46

mathaholic
Member
From: Earth
Registered: 2012-11-29
Posts: 3,247

### Re: Sexy primes

Are those about the "theorem" of the sexy primes? Whatever.

Mathaholic | 10th most active poster | Maker of the 350,000th post | Person | rrr's classmate

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## #21 2013-04-29 14:31:30

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,018

### Re: Sexy primes

Hi bobbym

It is the same proof. If you do not see that, it just means you haven't read my proof at all.

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #22 2013-04-29 15:40:42

Agnishom
Real Member
From: Riemann Sphere
Registered: 2011-01-29
Posts: 24,442
Website

### Re: Sexy primes

I am not getting bobbym's proof

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.

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## #23 2013-04-29 16:11:06

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 107,190

### Re: Sexy primes

Hi Agnishom;

boxes = multiples of 3, starting at 6. Dashes are the 2 numbers between every multiple of 3, like 16 and 17 is between 15 and 18. The lowest prime in our quadruplet has to be at position1 or position2.

Hi anonimnystefy;

I did not look at your proof because I was too busy writing up mine. I still think mine is easier to answer future questions and requires nothing but the ability to draw boxes and lines,

Did you see the question I asked in post#19? With mine, it is snap.

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.

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## #24 2013-04-29 21:28:18

ElainaVW
Member
Registered: 2013-04-29
Posts: 571

### Re: Sexy primes

Nice idea, I tried it on 2 4 4 4 4 2 and it worked fine.

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## #25 2013-04-29 21:35:14

bobbym
From: Bumpkinland
Registered: 2009-04-12
Posts: 107,190

### Re: Sexy primes

Hi;

Welcome to the forum! AdministratorM? bobbym is fine here. I am glad you tried it, just keep in mind that it is more useful for proving what doesn't work then what does.

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.

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