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jmc

number theory senior

Problem

Find the least positive four-digit solution of the congruence .
Solution
Add to both sides of the given congruence to obtain . We can multiply both sides by to get . Subtracting from the left-hand side and adding to the right-hand side gives . Thus for some integer . Solving , we find that is the smallest value of for which has four digits. Thus the minimum four-digit value of is .
Final answer
1016