The Stamp Collection

★ 5/10Diophantine Equations number theory Casework

Problem

Suppose that for some positive integer $n$ , using an unlimited supply of stamps worth $5$ , $n$ , and $n+1$ cents, the greatest postage that cannot be formed is exactly $91$ cents. Find the sum of all such positive integers $n$ .

Answer

Solution

Difficulty	5/10
Topics	Diophantine Equations, number theory, Casework

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