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number theory senior
Problem
Suppose , and are positive integers with , and , where and are integers and is not divisible by . What is the smallest possible value of ?
(A)
(B)
(C)
(D)
Solution
The power of for any factorial is given by the well-known algorithm It is rational to guess numbers right before powers of because we won't have any extra numbers from higher powers of . As we list out the powers of 5, it is clear that is less than 2006 and is greater. Therefore, set and to be 624. Thus, c is . Applying the algorithm, we see that our answer is .
Final answer
B