[Hint: Proceed by induction on n.] 16. Use the theory of congruences to verify that 89| 24 – 1 and 97| 248 – 1 - 17. Prove that whenever ab = cd (mod n) and b d (mod n), with ged(b, n) =

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Chapter2: Second-order Linear Odes
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16. Short and simplified.
58
ELEMENTARY NUMBER THEORY
n2 1, use congruence theory to establish each of the following divisibility
ements:
7152+3.25-2.
1313+2+42n+1.
(c) 2712 5m+1 + 5n+2_
(d) 4316*+2 + 72n+1.
4.3
One
speci
heart
to in
syste
inte
7. For n 2 1, show that
(-13)"+ = (-13)" +(-13)"- (mod 181)
[Hint: Notice that (-13)² = -13+1 (mod 181); use induction on n.]
8. Prove the assertions below:
(a) If a is an odd integer, then a? = 1 (mod 8).
(b) For any integer a, a³ = 0, 1, or 6 (mod 7).
(c) For any integer a, a“ = 0 or 1 (mod 5).
(d) If the integer a is not divisible by 2 or 3, then a? = 1 (mod 24).
9. If p is a prime satisfying n < p < 2n, show that
whe
the
If
2n
= 0 (mod p)
N
10. If a1, a2, ..., an is a complete set of residues modulon and gcd(a, n) = 1, prove that
aaj, aa2, . , aa, is also a complete set of residues modulo n.
[Hint: It suffices to show that the numbers in question are incongruent modulo n.]
11. Verify that 0, 1, 2, 2², 2³, ..., 2º form a complete set of residues modulo 11, but that
0, 12, 22, 3², .., 10² do not.
12. Prove the following statements:
(a) If gcd(a, n) = 1, then the integers
с, с +а,с +2а, с + За, ..., с + (п -1)а
form a complete set of residues modulo n for any c.
(b) Any n consecutive integers form a complete set of residues modulo n.
[Hint: Use part (a).]
(c) The product of any set of n consecutive integers is divisible by n.
13. Verify that if a = b (mod n¡) and a = b (mod n2), then a = b (mod n), where the integer
n = lcm(n1, n2). Hence, whenever n¡ and n2 are relatively prime, a = b (mod n¡n2).
14. Give an example to show that ak = bk (mod n) and k = j (mod n) need not imply that
a' = b (mod n).
15. Establish that if a is an odd integer, then for any n > 1
a" = 1 (mod 2"+2)
[Hint: Proceed by induction on n.]
16. Use the theory of congruences to verify that
89| 244 - 1
and
97 |248 – 1
17. Prove that whenever ab = cd (mod n) and
a =c (mod n).
18. If a =b (mod n1) and a =C (mod n2), prove that b c (mod n), where the integer
=d (mod n), with ged(b, n) = 1, then
%3D
n gcd(n1, n2).
Transcribed Image Text:58 ELEMENTARY NUMBER THEORY n2 1, use congruence theory to establish each of the following divisibility ements: 7152+3.25-2. 1313+2+42n+1. (c) 2712 5m+1 + 5n+2_ (d) 4316*+2 + 72n+1. 4.3 One speci heart to in syste inte 7. For n 2 1, show that (-13)"+ = (-13)" +(-13)"- (mod 181) [Hint: Notice that (-13)² = -13+1 (mod 181); use induction on n.] 8. Prove the assertions below: (a) If a is an odd integer, then a? = 1 (mod 8). (b) For any integer a, a³ = 0, 1, or 6 (mod 7). (c) For any integer a, a“ = 0 or 1 (mod 5). (d) If the integer a is not divisible by 2 or 3, then a? = 1 (mod 24). 9. If p is a prime satisfying n < p < 2n, show that whe the If 2n = 0 (mod p) N 10. If a1, a2, ..., an is a complete set of residues modulon and gcd(a, n) = 1, prove that aaj, aa2, . , aa, is also a complete set of residues modulo n. [Hint: It suffices to show that the numbers in question are incongruent modulo n.] 11. Verify that 0, 1, 2, 2², 2³, ..., 2º form a complete set of residues modulo 11, but that 0, 12, 22, 3², .., 10² do not. 12. Prove the following statements: (a) If gcd(a, n) = 1, then the integers с, с +а,с +2а, с + За, ..., с + (п -1)а form a complete set of residues modulo n for any c. (b) Any n consecutive integers form a complete set of residues modulo n. [Hint: Use part (a).] (c) The product of any set of n consecutive integers is divisible by n. 13. Verify that if a = b (mod n¡) and a = b (mod n2), then a = b (mod n), where the integer n = lcm(n1, n2). Hence, whenever n¡ and n2 are relatively prime, a = b (mod n¡n2). 14. Give an example to show that ak = bk (mod n) and k = j (mod n) need not imply that a' = b (mod n). 15. Establish that if a is an odd integer, then for any n > 1 a" = 1 (mod 2"+2) [Hint: Proceed by induction on n.] 16. Use the theory of congruences to verify that 89| 244 - 1 and 97 |248 – 1 17. Prove that whenever ab = cd (mod n) and a =c (mod n). 18. If a =b (mod n1) and a =C (mod n2), prove that b c (mod n), where the integer =d (mod n), with ged(b, n) = 1, then %3D n gcd(n1, n2).
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