Take a 6digit integer, abcdef, all of
whose digits are different. Then apply the process a*b^c + d*e^f to
generate a fourdigit unidigital integer (that is, one whose digits are
all the same). For example, this works with 237954 because 2 x 3^{7} + 9 x 5^{4} = 9999. Are there any other sixdigit integers which can be processed in this way to yield fourdigit unidigitals? 

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Last Updated: January 13th, 2010.