Proof of the Order Divisibility Property

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Discussion Overview

The discussion centers on the Order Divisibility Property in modular arithmetic, specifically addressing the proof that if \( a^n \equiv 1 \mod p \), then the order \( e_p(a) \) of \( a \) modulo \( p \) divides \( n \). Participants also explore conditions under which the congruence \( a^m \equiv a^n \mod p \) holds when \( a \) is relatively prime to \( p \.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant states the Order Divisibility Property and seeks a proof for it.
  • Another participant suggests using the division algorithm to express \( n \) in terms of \( e_p(a) \) and a remainder \( r \), questioning what can be inferred about \( r \).
  • A participant asserts that \( r \) must equal zero but expresses uncertainty about how to demonstrate this.
  • Discussion arises regarding the order \( e_p(a) \) when \( a \) is relatively prime to \( p \), with one participant proposing it could be \( p-1 \), while another counters that other integers less than \( p-1 \) could also satisfy the condition.
  • Another participant references the division algorithm, indicating that \( 0 \leq r < e_p(a) \) and prompts further exploration of this relationship.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the division algorithm and the nature of the order \( e_p(a) \). There is no consensus on the proofs or the specific values of \( e_p(a) \) in relation to \( p \).

Contextual Notes

Participants have not fully resolved the mathematical steps required to prove the Order Divisibility Property or the conditions for the congruence \( a^m \equiv a^n \mod p \). The discussion reflects varying interpretations of the definitions and properties involved.

squire636
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The Order Divisibility Property states that if an = 1 (mod p), then the order ep(a) of a (mod p) divides n.

How can I go about proving this?

Additionally, if a is relatively prime to p, when does the congruence am = an (mod p) hold? Is there a proof for this as well?

Thanks!
 
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Hint for 1: The division algorithm says we can write ##n=qe_p(a)+r##. What can you say about r?

Hint for 2: If a is relatively prime to p, what is ##e_p(a)##?
 
For the first one, r must equal zero, but I'm not sure how to show that it is true.

For the second, would the order ep(a) = p-1 ?
 
squire636 said:
For the second, would the order ep(a) = p-1 ?

Not really; other integer less than p-1 could do the trick. Anyway, I believe morphism was simply trying to make you think about the very definition of 'order'. And what would you need to do to this definition in order to transform it into something like the premises that you are given.
 
As for the first problem, the division algorithm tells us that ##0 \leq r < e_p(a)##. What can you do with this, squire636?
 

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