5. Use Kraitchik's factorization method to factor 11653.

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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**Mathematical Problems on Number Theory**

1. **Use Euler’s Theorem** to prove \( a^{265} \equiv a \pmod{105} \) for all \( a \in \mathbb{Z} \).

2. **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** to prove \( (6(k - 4)!) \equiv 1 \pmod{k} \), if \( k \) is prime.

4. **Use Fermat’s factorization method** to factor 2168495737.

5. **Use Kraitchik’s factorization method** to factor 11653.

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

7. **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. 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:**Mathematical Problems on Number Theory** 1. **Use Euler’s Theorem** to prove \( a^{265} \equiv a \pmod{105} \) for all \( a \in \mathbb{Z} \). 2. **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** to prove \( (6(k - 4)!) \equiv 1 \pmod{k} \), if \( k \) is prime. 4. **Use Fermat’s factorization method** to factor 2168495737. 5. **Use Kraitchik’s factorization method** to factor 11653. 6. Prove \( \phi(k^2) = k \cdot \phi(k) \) for all \( k \in \mathbb{N} \). 7. **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. 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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