The answer to this question is `10^5`. Instead of finding a six digit number with two different digits in any two numbers, find a 5 digit number with 1 different digit in any two numbers (which will always have a different digit between 2 numbers) and just add the last digit in the units place. This 5 digit number can be anything from 0 to 99999 and can be done in `10^5` ways. The `6^(th)` digit is obtained by adding the first 5 digits and taking the units place of the sum.
