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Let (x, y, z) be a primitive Pythagorean triple

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MIDTERM: SOME PROBLEMS FROM PREVIOUS YEARS

1. Find all integers x, y satisfying the following equation:

98x+ 68y= 2.

2. Solve the system of congruence equation:

(3x≡1 (mod23) 2x≡9 (mod17)

3. What is the remainder of 2124 when divided by 41?

4. What are all the primes p < 14 for which x12 ≡ 1 (mod p) is valid for all x such that(x, p) = 1?

5. Which of the following functions is multiplicative? Why?

(a) σ(n) (the sum of divisors function);

(b) φ(n)2; (c) φ(n) + 1?

6. Let (x, y, z) be a primitive Pythagorean triple. Is it possible that x≡2(mod 8)? Why?

7. Let p, q be distinct prime numbers, let α, β be positive integers and let n = pαqβ. Assume that the productα·β is even. Is it possible that the number of divisorsτ(n)of nis divisible by four: 4|τ(n)? If your answer is ’yes’, provide an example. If your answer is ’no’, provide an explanation.

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