The number of strings of six characters (uppercase alphabets and numbers) out of which at least one character should be a number. This problem is often solved like this:
All strings of $6$ digits made up of uppercase characters and numbers $= 36^6$.
All strings of $6$ digits with only uppercase characters = $26^6$.
Answer $= 36^6 - 26^6 = 1867866560$.
I was searching for a way to do this not through the subtraction way as above.