Number Theory: Find Multiplicative Order for (a,n) = 1

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SUMMARY

The discussion centers on finding the multiplicative order \( k \) for integers \( a \) and \( n \) where \( (a,n) = 1 \). It is established that \( a^{\phi(n)} \equiv 1 \mod n \) according to Euler's totient function \( \phi(n) \), but \( \phi(n) \) does not always yield the smallest \( k \). Participants agree that \( k \) must be a divisor of \( \phi(n) \) and highlight that there is no general formula for determining \( k \) except in specific cases such as \( a \equiv \pm 1 \mod n \). The discussion concludes that brute force remains the most effective method for finding \( k \) in general scenarios.

PREREQUISITES
  • Understanding of Euler's totient function \( \phi(n) \)
  • Knowledge of modular arithmetic
  • Familiarity with primitive roots in number theory
  • Basic concepts of divisors and their properties
NEXT STEPS
  • Research the properties of Euler's totient function \( \phi(n) \)
  • Learn about primitive roots and their significance in number theory
  • Explore algorithms for brute force computation of multiplicative orders
  • Study specific cases where \( k \) can be determined directly from \( a \) and \( n \)
USEFUL FOR

This discussion is beneficial for mathematicians, number theorists, and students studying advanced topics in number theory, particularly those interested in multiplicative orders and Euler's totient function.

SeReNiTy
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Hey guys, I've been studying some number theory recently and have a question. We know if (a,n) = 1 then a^phi(n) is congruent to 1 (mod n)

where phi(n) = euler's totient function

Now my question is the totient function does not always return the smallest possible integer such that a^k is congruent to 1. So how do i find k if phi(n) does not equal k?
 
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SeReNiTy said:
Hey guys, I've been studying some number theory recently and have a question. We know if (a,n) = 1 then a^phi(n) is congruent to 1 (mod n)

where phi(n) = euler's totient function

Now my question is the totient function does not always return the smallest possible integer such that a^k is congruent to 1. So how do i find k if phi(n) does not equal k?
k would be a divisor of phi(n) but as far as I know there is no known formula for specific n and a except for a = +/-1 mod n in which case k = 1 or 2.
 
SeReNiTy said:
So how do i find k if phi(n) does not equal k?
The numbers that has phi(n) as there orders are called primitive roots. It is still an unresolved problem in mathematics, i.e. how to determine the primitive roots of numbers. (However, something about special cases are known).

Thus, brute force is the best way to go.
 

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