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Problem Sheet III
1. Solve the linear congruences (i) 2x ≡ 4 (mod 7), (ii) 6x ≡ 3 (mod 21).
Use (i) or otherwise to find all integers x, y such that 2x+ 7y = 53.
2. Prove the converse of Wilson’s Theorem: for n > 1 composite,
[Hint: show that n|(n−1)! unless n = 4 and treat n = 4 separately.]
3. Find all solutions of the simultaneous congruences
4. Find the remainder when 235042 is divided by 37.
5. Let n ∈ N such that n ≡ 3 (mod 4). Show that n cannot be written as the sum of two squares.
Show further that a positive integer ≡ 7 (mod 8) cannot be written as the sum of three squares.
Any guesses for sums of four squares?