What Are Alternative Infinite Sets of Coprimes Generated by Simple Functions?

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Discussion Overview

The discussion revolves around identifying alternative infinite sets of coprimes generated by simple functions, exploring various mathematical sequences and their properties. Participants are particularly interested in defining formulas that yield the nth term of such sets.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about infinite sets of coprimes beyond Sylvester's sequence, defined as S(n)=S(n-1)*(S(n-1)-1)+1, with S(0)=2.
  • Another suggests that the primes could be considered, although this is met with skepticism regarding their relevance.
  • There is a proposal to consider primes that are congruent to 1 mod 4 or products of certain pairs of primes as potential coprime sets.
  • A participant expresses a desire for a set along with a defining formula for the nth term, prompting further discussion on the nature of such formulas.
  • One participant mentions the expression 2^n - 1 as a means to demonstrate the existence of infinitely many primes, noting that consecutive terms are coprime.
  • Another participant challenges the coprimality of certain terms derived from 2^n - 1, leading to a clarification that only consecutive terms are coprime.
  • A proposed formula for generating coprimes is a(n) = 5*2^(2n) + 5*2^n + 1, with a request for proof or disproof of its validity.
  • Concerns are raised about the divisibility of terms generated by the proposed formula, suggesting that they may not always yield coprimes.
  • A participant expresses appreciation for a specific reply that aligns with their inquiry but notes that restricting n to prime numbers renders the formula ineffective for their purpose.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a specific set of coprimes or a universally accepted formula. Multiple competing views and uncertainties regarding the properties of proposed sequences remain evident throughout the discussion.

Contextual Notes

Some limitations include the lack of definitive proofs for the proposed formulas and the unresolved nature of the coprimality of certain terms. The discussion also highlights dependencies on specific definitions and conditions for the sequences mentioned.

kureta
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[SOLVED] infinite set of coprimes

does anyone know an infinite set of coprimes except for the elements of sylvester's sequence. S(n)=S(n-1)*(S(n-1)-1)+1, with s(0)=2
 
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The primes, maybe? :P
 
yesss

yes. thanks but... well... nevermind:rolleyes:
 
The primes = 1 mod 4? The noncomposites? {2*3, 5*7, 11*13, 17*19, ...}?
 
then i should change my question

does anyone know such a set AND its defining formula which gives us the nth term.
 
kureta said:
does anyone know such a set AND its defining formula which gives us the nth term.

The primes have many defining formulas, a fair number of which use only basic operations (say, addition, multiplication, factorials, and sine). To what end do you want this?
 
I don't have a reference to hand, but you can consider things like 2^n - 1. Indeed that is one proof that there are infintitely many primes.

Note 2^n - 1 = 2*(2^{n-1} -1) + 1, proving that they are coprime.
 
2^2-1=3 and 2^4-1=15 and 15/3=5 so they are not all coprimes am i wrong?
 
Sorry, my mistake - consecutive terms are coprime, not every term. Duh. But there is something to do with things like this that demonstrates infinitely many primes by producing coprimes. I don't have the reference to hand (I read it in 'Proofs from the Book' by Aigner and Ziegler).
 
  • #10
kureta said:
does anyone know such a set AND its defining formula which gives us the nth term.
a(n) = 5*2^(2n) +5*2^n + 1 is my guess. Prove or disprove
One thing that is certain, they can only be divisible by a prime ending in 1 or 9
 
  • #11
ramsey2879 said:
a(n) = 5*2^(2n) +5*2^n + 1 is my guess. Prove or disprove
One thing that is certain, they can only be divisible by a prime ending in 1 or 9
Forget this too, If n = 8 2^n equals 9 and 2^2n = 4 mod 11.
5*(4+9) + 1 = 66. also there are other powers of 2 with the same residue mod 11 so those values for n give a(n) which are not coprime.
Maybe take n to be prime for the n in a(n) or something similar.
 
  • #12
ramsey2879 you're the man

ramsey2879 your reply was the kind that i was looking for. thanks. but taking n to be prime makes this formula useless for me. because my purpose is to find a set of coprimes generated by a simple function . and you should see "a different approach to primes" thread for the reason of my asking for such a set.
 

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