How many 6 digit number combinations are there?

The smallest 6-digit number is 100,000.

The largest 6-digit number is 999,999.

If you count from the smallest one to the largest one, you'll name

every possible one.

But that's exactly the same thing as counting from 1 to 999,999 except

skipping the first 99,999 because they don't have enough digits.

So you're left with (999,999 minus 99,999) = 900,000 numbers remaining

999999 * 2 if you want to include the negatives