MathDB
7-10 Doubles

Source:

December 6, 2005
AMCAIME

Problem Statement

Call a positive integer NN a <spanclass=′latex−italic′>7−10double</span><span class='latex-italic'>7-10 double</span> if the digits of the base-7 representation of NN form a base-10 number that is twice N.N. For example, 51 is a 7-10 double because its base-7 representation is 102. What is the largest 7-10 double?
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