Math Is Fun Forum

phanthanhtom

Member

Registered: 2012-06-22

Posts: 290

Prime numbers

Find all sets of 4 different prime numbers (a, b, c, d) with

such that the sum of any three out of these four primes are also prime.
In other words, find positive integers a, b, c, d such that a, b, c, d, a+b+c, a+b+d, a+c+d and b+c+d are eight different primes.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Prime numbers

Hi phanthanhtom;

First thing you have to do is change this:

because of this

Find all sets of 4 different prime numbers (a, b, c, d)

And I am finding many solutions. Perhaps there are an infinite number. Or perhaps something is wrong in my method.

---

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.

phanthanhtom

Member

Registered: 2012-06-22

Posts: 290

Re: Prime numbers

There might be an infinite number of solutions. I think so.
And there might be two pairs of the same numbers. Or a = b and c = d. As long as not all of them are the same. (In fact I acknowledge that that sentence is redundant)

phanthanhtom

Member

Registered: 2012-06-22

Posts: 290

Re: Prime numbers

One more problem:
I have checked  the prime numbers table <6000. The number of prime quadruplets are 9 (excluding 5-7-11-13), and the number of near-quadruplets (i.e. exactly one number missing, if this number is added it makes a 10k+1, 10k+3, 10k+7 and 10k+9 quadruplet) is 37.
37/9=4.25 rounds to 4 = 4C3 (combination without repetition). Interesting!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Prime numbers

{{a, b, c,   d}}
{{5, 7, 17, 19}},
{{5, 7, 19, 47}},
{{5, 7, 29, 67}},
{{5, 7, 31, 71}},
{{5, 7, 41, 61}},
{{5, 7, 61, 71}},
{{5, 11, 13, 43}},
{{5, 11, 31, 37}},
{{5, 11, 31, 67}},
{{5, 13, 19, 29}},
{{5, 13, 23, 43}},
{{5, 13, 23, 61}},
{{5, 13, 41, 43}},
{{5, 13, 43, 53}},
{{5, 17, 19, 37}},
{{5, 17, 31, 61}},
{{5, 19, 37, 47}},
{{5, 23, 31, 43}},
{{5, 23, 43, 61}},
{{5, 31, 37, 71}},
{{5, 31, 43, 53}},
{{5, 31, 47, 61}},
{{5, 31, 61, 71}},
{{5, 37, 41, 61}},
{{5, 37, 59, 67}},
{{7, 11, 13, 23}},
{{7, 11, 19, 41}},
{{7, 11, 19, 53}},
{{7, 11, 19, 71}},
{{7, 11, 29, 43}},
{{7, 11, 29, 61}},
{{7, 11, 41, 61}},
{{7, 11, 43, 53}},
{{7, 13, 17, 23}},
{{7, 13, 17, 59}},
{{7, 13, 23, 53}},
{{7, 13, 41, 53}},
{{7, 13, 41, 59}},
{{7, 13, 47, 53}},
{{7, 17, 19, 47}},
{{7, 17, 23, 43}},
{{7, 17, 29, 37}},
{{7, 17, 29, 43}},
{{7, 17, 37, 59}},
{{7, 17, 43, 47}},
{{7, 19, 41, 53}},
{{7, 23, 29, 31}},
{{7, 23, 29, 37}},
{{7, 23, 31, 59}},
{{7, 23, 37, 53}},
{{7, 29, 31, 71}},
{{7, 29, 53, 67}},
{{7, 31, 41, 59}},
{{7, 43, 47, 59}},
{{7, 59, 61, 71}},
{{11, 13, 17, 43}},
{{11, 13, 19, 29}},
{{11, 13, 23, 37}},
{{11, 13, 37, 59}},
{{11, 13, 43, 47}},
{{11, 17, 19, 31}},
{{11, 17, 19, 43}},
{{11, 17, 31, 61}},
{{11, 19, 23, 37}},
{{11, 19, 23, 67}},
{{11, 19, 29, 31}},
{{11, 19, 31, 59}},
{{11, 19, 37, 41}},
{{11, 19, 37, 53}},
{{11, 19, 53, 67}},
{{11, 19, 67, 71}},
{{11, 29, 31, 67}},
{{11, 29, 61, 67}},
{{11, 31, 37, 41}},
{{11, 31, 37, 59}},
{{11, 31, 59, 61}},
{{11, 31, 59, 67}},
{{11, 37, 41, 61}},
{{11, 37, 59, 61}},
{{13, 17, 23, 31}},
{{13, 17, 23, 43}},
{{13, 17, 23, 67}},
{{13, 17, 29, 37}},
{{13, 17, 29, 67}},
{{13, 17, 31, 53}},
{{13, 17, 31, 59}},
{{13, 17, 37, 53}},
{{13, 17, 37, 59}},
{{13, 17, 41, 43}},
{{13, 17, 43, 53}},
{{13, 17, 43, 71}},
{{13, 19, 29, 41}},
{{13, 19, 41, 47}},
{{13, 19, 47, 71}},
{{13, 23, 31, 53}},
{{13, 23, 37, 47}},
{{13, 23, 37, 53}},
{{13, 23, 43, 47}},
{{13, 23, 43, 71}},
{{13, 23, 47, 67}},
{{13, 23, 53, 61}},
{{13, 29, 37, 47}},
{{13, 29, 67, 71}},
{{13, 37, 47, 53}},
{{13, 41, 43, 47}},
{{13, 41, 43, 53}},
{{13, 43, 53, 71}},
{{17, 19, 23, 31}},
{{17, 19, 23, 61}},
{{17, 19, 23, 67}},
{{17, 19, 31, 53}},
{{17, 19, 37, 47}},
{{17, 19, 37, 53}},
{{17, 19, 43, 47}},
{{17, 19, 53, 67}},
{{17, 19, 61, 71}},
{{17, 29, 37, 43}},
{{17, 29, 43, 67}},
{{17, 31, 59, 61}},
{{17, 37, 43, 47}},
{{17, 43, 47, 67}},
{{17, 43, 53, 67}},
{{19, 23, 29, 31}},
{{19, 23, 29, 61}},
{{19, 23, 31, 47}},
{{19, 23, 31, 59}},
{{19, 23, 37, 41}},
{{19, 23, 37, 47}},
{{19, 23, 37, 71}},
{{19, 23, 41, 67}},
{{19, 23, 47, 61}},
{{19, 29, 31, 53}},
{{19, 29, 59, 61}},
{{19, 37, 41, 53}},
{{19, 37, 41, 71}},
{{19, 41, 43, 47}},
{{19, 41, 67, 71}},
{{19, 47, 61, 71}},
{{19, 59, 61, 71}},
{{23, 37, 43, 47}},
{{23, 37, 43, 71}},
{{23, 37, 47, 67}},
{{23, 43, 47, 61}},
{{29, 31, 37, 41}},
{{29, 31, 37, 71}},
{{29, 31, 41, 67}},
{{29, 31, 53, 67}},
{{29, 37, 41, 61}},
{{29, 41, 43, 67}},
{{31, 37, 41, 59}},
{{31, 41, 59, 67}},
{{31, 47, 59, 61}},
{{31, 47, 61, 71}},
{{37, 43, 59, 71}},
{{37, 47, 53, 67}},
{{37, 53, 59, 61}},
{{37, 53, 59, 67}},
{{43, 47, 59, 61}},
{{43, 53, 67, 71}}

That is just for primes up to 71. Looks like there is an infinite number. I can see no reason why it should stop.

---

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.