Puzzle #130: Secret Number

I am thinking of a three-digit number. Of the numbers that fit the other clues, the solution is the one with the largest prime factor. The sum of two of the digits is equal to the third digit. None of the digits are 1, prime, or 0. What is the number?

Submit your answer to Gene Wirchenko <genew@telus.net>. Your answer should be in the form of a proof. That means to show how your answer must be correct. The deadline is Wednesday, December 2, 2015 at noon Pacific Time. I will post the answer shortly after.