Math Problem Statement

How many numbers smaller than 121 are there that are prime to 121?

Solution

To determine how many numbers smaller than 121 are prime to 121, we need to find the number of integers less than 121 that are coprime to 121. This is done using Euler's Totient Function, denoted as ϕ(n)\phi(n), which counts the number of integers less than nn that are relatively prime to nn.

Steps:

  1. Factorization of 121: 121=112121 = 11^2 The prime factor of 121 is 11.

  2. Euler's Totient Function: For n=pkn = p^k, where pp is a prime number and kk is a positive integer, Euler's Totient Function is given by: ϕ(pk)=pk(11p)\phi(p^k) = p^k \left( 1 - \frac{1}{p} \right)

    Applying this to 121=112121 = 11^2: ϕ(121)=121(1111)=121×1011=110\phi(121) = 121 \left( 1 - \frac{1}{11} \right) = 121 \times \frac{10}{11} = 110

Conclusion:

There are 110 numbers smaller than 121 that are prime (relatively prime or coprime) to 121.

Would you like more details or further explanations?

Here are 5 related questions you might find useful:

  1. What is Euler's Totient Function and how is it calculated for composite numbers?
  2. How can we find the prime factorization of a number efficiently?
  3. What are the properties of numbers that are coprime to a given number?
  4. How does Euler's Totient Function help in cryptography, specifically in RSA encryption?
  5. Can Euler's Totient Function be extended to larger numbers with more prime factors?

Tip: The Euler's Totient Function is multiplicative, meaning ϕ(mn)=ϕ(m)×ϕ(n)\phi(mn) = \phi(m) \times \phi(n) when mm and nn are coprime!

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Math Problem Analysis

Mathematical Concepts

Number Theory
Coprime Numbers
Euler's Totient Function

Formulas

Euler's Totient Function: φ(n) = n * (1 - 1/p) for n = p^k
φ(121) = 121 * (1 - 1/11) = 110

Theorems

Euler's Totient Theorem

Suitable Grade Level

Grades 9-12