2. Use Fermat's Little Theorem, or its corollary, to find the units digit of 72018 + 112019 + 132020 + 132021 + 172022

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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### Mathematics Problem Set

1. **Use Euler’s Theorem**

   Prove \( a^{265} \equiv a \pmod{105} \) for all \( a \in \mathbb{Z} \).

2. **Use Fermat’s Little Theorem**

   Use Fermat’s Little Theorem, or its corollary, to find the units digit of:
   \[
   7^{2018} + 11^{2019} + 13^{2020} + 13^{2021} + 17^{2022}
   \]

3. **Use Wilson’s Theorem**

   Use Wilson’s Theorem to prove \( (6(k - 4))! \equiv 1 \pmod{k} \), if \( k \) is prime.

4. **Factorization Using Fermat’s Method**

   Use Fermat’s factorization method to factor 2168495737.

5. **Factorization Using Kraitchik’s Method**

   Use Kraitchik’s factorization method to factor 11653.

6. **Prove the Following Function**

   Prove \( \phi(k^2) = k \cdot \phi(k) \) for all \( k \in \mathbb{N} \).

7. **Proofs Based on Number Properties**

   Prove each of the following statements:

   (a) If \( q \) is a prime number not equal to 3 and \( k = 3q \), then \( \sigma(k) = 2(\tau(k) + \phi(k)) \).

   (b) If \( q \) is an odd prime number and \( k = 2q \), then \( k = \sigma(k) - \tau(k) - \phi(k) \).

8. **Inverse Modulo Proof**

   Let \( \hat{a} \) be the inverse of \( a \) modulo \( k \). Prove that the order of \( a \) modulo \( k \) is equal to the order of \( \hat{a} \) modulo \( k \). Use this result to easily show that if \( a \) is a primitive root modulo \( k \) then \( \hat{a} \) is also a primitive root modulo \( k \).
Transcribed Image Text:### Mathematics Problem Set 1. **Use Euler’s Theorem** Prove \( a^{265} \equiv a \pmod{105} \) for all \( a \in \mathbb{Z} \). 2. **Use Fermat’s Little Theorem** Use Fermat’s Little Theorem, or its corollary, to find the units digit of: \[ 7^{2018} + 11^{2019} + 13^{2020} + 13^{2021} + 17^{2022} \] 3. **Use Wilson’s Theorem** Use Wilson’s Theorem to prove \( (6(k - 4))! \equiv 1 \pmod{k} \), if \( k \) is prime. 4. **Factorization Using Fermat’s Method** Use Fermat’s factorization method to factor 2168495737. 5. **Factorization Using Kraitchik’s Method** Use Kraitchik’s factorization method to factor 11653. 6. **Prove the Following Function** Prove \( \phi(k^2) = k \cdot \phi(k) \) for all \( k \in \mathbb{N} \). 7. **Proofs Based on Number Properties** Prove each of the following statements: (a) If \( q \) is a prime number not equal to 3 and \( k = 3q \), then \( \sigma(k) = 2(\tau(k) + \phi(k)) \). (b) If \( q \) is an odd prime number and \( k = 2q \), then \( k = \sigma(k) - \tau(k) - \phi(k) \). 8. **Inverse Modulo Proof** Let \( \hat{a} \) be the inverse of \( a \) modulo \( k \). Prove that the order of \( a \) modulo \( k \) is equal to the order of \( \hat{a} \) modulo \( k \). Use this result to easily show that if \( a \) is a primitive root modulo \( k \) then \( \hat{a} \) is also a primitive root modulo \( k \).
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