Are Two Successive Integers Always Coprime?

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Discussion Overview

The discussion centers around the question of whether the greatest common divisor (gcd) of two successive integers, specifically (n, n+1), is always equal to 1, thereby determining if they are coprime. The context includes aspects of logic and proof, with references to formal proof techniques.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested, Homework-related

Main Points Raised

  • One participant questions whether the gcd of two successive integers is always 1 and seeks a proof for this assertion.
  • Another participant expresses agreement with the idea that they are coprime but does not provide a proof.
  • A different participant asks for a method to prove the claim, suggesting the use of Euclid's Algorithm.
  • One participant proposes a reasoning approach, stating that if an integer m divides n, then n+1 cannot be divisible by m unless m equals 1, implying that n and n+1 are coprime.
  • Another participant mentions a proof related to this property that demonstrates the existence of infinitely many primes.
  • One participant comments on the number of replies, suggesting that trivial inquiries tend to attract more responses.
  • A participant speculates that a formal proof starting from Peano's axioms would be necessary, estimating it could take about 50 lines to construct.
  • Another participant reiterates the idea that trivial inquiries receive more replies due to broader familiarity with the topic.

Areas of Agreement / Disagreement

Participants generally agree that two successive integers are coprime, but the discussion remains unresolved regarding the formal proof and the depth of the inquiry.

Contextual Notes

The discussion includes references to formal proof techniques and assumptions about knowledge levels, but lacks a definitive proof or resolution of the inquiry.

smithg86
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is the gcd of two successive integers (n, n+1) always equal to 1? i.e., are two successive integers always coprime? it seems like this is the case, but how would you prove this? (this came up in my logic/proof class, but the professor wouldn't or couldn't prove it - this isn't a HW question.)
 
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yes, i think so.
 
but how would you prove it to be true?
 
try Euclid's Algorithm...
 
Isn't it pretty obvious? suppose m divides n, then n=jm for some j. But then n+1=jm+1 which is not divisible by m (unless m=1). Thus n and n+1 are coprime.
 
It's neat that you brought that up.

I saw a proof using this property to show that there are infinitely many primes.
 
how can there be 5 replies to this question?

the more trivial the inquiry the more replies.
 
If this comes from a logic class, then I'm assuming you need to construct a formal proof starting from Peano's axioms, with the "existential introduction/elimination", etc. This proposition should take about 50 lines to prove, if you're lucky.
 
mathwonk said:
the more trivial the inquiry the more replies.

Duh! Because more people know the answer.
 

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