9. Show that there are infinitely many primes of the form 16k + 1. More generally, show that for any r > 0, there are infinitely many primes of the form 2" k + 1. 10

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Chapter8: Sequences, Series, And Probability
Section8.5: Mathematical Induction
Problem 37E
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Can you do #9?
ler's Phi
Exercises for Section 4.1
. Use Fermat's Theorem to compute the following quantities.
(a) 31100 mod 19.
(b) 210000 mod 29.
(c) 99999 mod 31.
2. Show that 1184 – 584 is divisible by 7.
3. Show that if n = 2 (mod 4), then 9" + 8" is divisible by 5.
4. For which values of n is 3" + 2" divisible by 13? by 7?
5. Use Fermat's Theorem to show that n13
- n is divisible by 2730 for all n.
6. Show that if p > 3 is prime, then ab"
baP is divisible by 6p.
-
7. Show, using the Binomial Theorem, that if p is prime and a and b are inte-
gers, then (a + b)P = a + b (mod p).
8. Show that no prime number of the form 4k + 3 can divide a number of the
form n2 + 1.
9. Show that there are infinitely many primes of the form 16k + 1. More
generally, show that for any r > 0, there are infinitely many primes of the
form 2" k + 1.
10. Let n = r4 +1. Show that 3, 5, and 7 cannot divide n. What is the smallest
prime that can divide n? Determine the form of the prime divisors of n.
11. Show that any proper factor, whether prime or not, of a composite Mersenne
number 2P – 1 is of the form 1 + 2pk for some k.
12. What can you say about the prime factors of a composite Fermat number
Fn = 22" +1? Use Fermat's Theorem and Proposition 4.1.5 to find a factor
of F5, thereby disproving Fermat's statement that all the Fn are prime.
13. In 1909, Wiefrich proved that if p is prime and xP + yP = zP has integer
solutions withpł xyz, thenp satisfies 2P! = 1 (mod p²). A prime p
satisfying this latter congruence is called a Wiefrich prime. Determine the
first two Wiefrich primes.
Transcribed Image Text:ler's Phi Exercises for Section 4.1 . Use Fermat's Theorem to compute the following quantities. (a) 31100 mod 19. (b) 210000 mod 29. (c) 99999 mod 31. 2. Show that 1184 – 584 is divisible by 7. 3. Show that if n = 2 (mod 4), then 9" + 8" is divisible by 5. 4. For which values of n is 3" + 2" divisible by 13? by 7? 5. Use Fermat's Theorem to show that n13 - n is divisible by 2730 for all n. 6. Show that if p > 3 is prime, then ab" baP is divisible by 6p. - 7. Show, using the Binomial Theorem, that if p is prime and a and b are inte- gers, then (a + b)P = a + b (mod p). 8. Show that no prime number of the form 4k + 3 can divide a number of the form n2 + 1. 9. Show that there are infinitely many primes of the form 16k + 1. More generally, show that for any r > 0, there are infinitely many primes of the form 2" k + 1. 10. Let n = r4 +1. Show that 3, 5, and 7 cannot divide n. What is the smallest prime that can divide n? Determine the form of the prime divisors of n. 11. Show that any proper factor, whether prime or not, of a composite Mersenne number 2P – 1 is of the form 1 + 2pk for some k. 12. What can you say about the prime factors of a composite Fermat number Fn = 22" +1? Use Fermat's Theorem and Proposition 4.1.5 to find a factor of F5, thereby disproving Fermat's statement that all the Fn are prime. 13. In 1909, Wiefrich proved that if p is prime and xP + yP = zP has integer solutions withpł xyz, thenp satisfies 2P! = 1 (mod p²). A prime p satisfying this latter congruence is called a Wiefrich prime. Determine the first two Wiefrich primes.
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