1. Let a, b and c integers. Prove or disprove the next statements: a. 7|a" – a b. If 7|a? + b² then 7|a and 7|b c. If 7|a? + b³ + c³ then 7|abc

Elements Of Modern Algebra
8th Edition
ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter2: The Integers
Section2.2: Mathematical Induction
Problem 50E: Show that if the statement 1+2+3+...+n=n(n+1)2+2 is assumed to be true for n=k, the same equation...
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1,2, and 6 only. Comes from the textbook, Elementary Number Theory 6th edition. Thank you!

Many of the next problems can be done by using remainders or congruency, either way is fine with me.
1. Let a, b and c integers. Prove or disprove the next statements:
a. 7|a" – a
b. If 7|a? + b? then 7|a and 7|b
c. If 7|a? + b3 + c³ then 7|abc
2. Prove that there is no integer n such that 7|4n2 – 3.
3. Find the remainder by division by 7 of 99999999.
4. Find the remainder in the division by 17 of 15!
5. Let p be a prime. Show that for all integer a we have that p|a® + (p – 1)! a and
pla + (p – 1)! aP
Next some problems not directly related with congruencies but typical of arithmetic.
6. Five men collected several coconuts from a deserted island, and they decided to divide the
coconuts the next day. During the night, one of them decided to separate his part so he divided
the total in 5 groups and give the left-over coconut to a nearby monkey, the man went to sleep.
Next, another man did the same with the remainders coconuts and give the left-over coconut to
the monkey. During the night, every man did the same. Next morning the men divide the
remainder coconuts and give the left-over coconut to the monkey. Question: What is the
minimum number of original coconuts?
7. Ihave weights that weight power of 2 kilograms, like 1, 2, 4, 8, 16,..kilograms. Which weights
are necessary to weight 213 kilograms?
A slightly more advance ideas.
8. As we know the equation ax = 1 (mod n) can be solve if and only if (a, n) = 1, so a and n are
relatively prime. So, knowing the elements relatively prime to another is somewhat important.
Let us call (n) the number of positive elements less than n that are relatively prime with n.
Prove the next claims about p.
a. If p is prime, what is p (p)?
b. If p is prime, what is o (p")?
c. Ifp and q are prime, what is o(pq)?
Transcribed Image Text:Many of the next problems can be done by using remainders or congruency, either way is fine with me. 1. Let a, b and c integers. Prove or disprove the next statements: a. 7|a" – a b. If 7|a? + b? then 7|a and 7|b c. If 7|a? + b3 + c³ then 7|abc 2. Prove that there is no integer n such that 7|4n2 – 3. 3. Find the remainder by division by 7 of 99999999. 4. Find the remainder in the division by 17 of 15! 5. Let p be a prime. Show that for all integer a we have that p|a® + (p – 1)! a and pla + (p – 1)! aP Next some problems not directly related with congruencies but typical of arithmetic. 6. Five men collected several coconuts from a deserted island, and they decided to divide the coconuts the next day. During the night, one of them decided to separate his part so he divided the total in 5 groups and give the left-over coconut to a nearby monkey, the man went to sleep. Next, another man did the same with the remainders coconuts and give the left-over coconut to the monkey. During the night, every man did the same. Next morning the men divide the remainder coconuts and give the left-over coconut to the monkey. Question: What is the minimum number of original coconuts? 7. Ihave weights that weight power of 2 kilograms, like 1, 2, 4, 8, 16,..kilograms. Which weights are necessary to weight 213 kilograms? A slightly more advance ideas. 8. As we know the equation ax = 1 (mod n) can be solve if and only if (a, n) = 1, so a and n are relatively prime. So, knowing the elements relatively prime to another is somewhat important. Let us call (n) the number of positive elements less than n that are relatively prime with n. Prove the next claims about p. a. If p is prime, what is p (p)? b. If p is prime, what is o (p")? c. Ifp and q are prime, what is o(pq)?
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