|Take a 6-digit integer, abcdef, all of
whose digits are different. Then apply the process a*b^c + d*e^f to
generate a four-digit unidigital integer (that is, one whose digits are
all the same).
For example, this works with 237954 because 2 x 37 + 9 x 54 = 9999. Are there any other six-digit integers which can be processed in this way to yield four-digit unidigitals?