We look at the division of 673209 by 81 
The aim is to understand the frequency of 81 in 673209.

Advancing to step 1:
The number 81 fits into 6 0 times, leaving a remainder of 6.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 6, we get 6.
Take the next digit (7) from the dividend and append it to 6, then repeat: 67 / 81

Moving on to step 2:
When dividing 67 by 81, we get 0 with a remainder of 67.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we take 0 away from 67, we end up with 67.
Grab the next digit (3) from the dividend, add it to 67, then carry on: 673 / 81

Going ahead to step 3:
The number 81 fits into 673 8 times, leaving a remainder of 25.
Record the quotient 8 as the next digit in the result. 
Result so far: 8.0
Subtracting 648 from 673 leaves us with 25.
Bring next digit (2) of the dividend behind the 25 and repeat the process: 252 / 81

Step 4:
If we divide 252 by 81, we get 3 and a remainder of 9.
The next digit of our result is 3. 
Result so far: 83.0
Subtracting 243 from 252 leaves us with 9.
Grab the next digit (0) from the dividend, add it to 9, then carry on: 90 / 81

Going ahead to step 5:
When dividing 90 by 81, we get 1 with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 831.0
If we take 81 away from 90, we end up with 9.
Append the next digit (9) from the dividend to 9 and continue with: 99 / 81

Moving on to step 6:
99 divided by 81 is 1 with a remainder of 18.
The next digit of our result is 1. 
Result so far: 8311.0
If we take 81 away from 99, we end up with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Advancing to step 7:
The number 81 fits into 180 2 times, leaving a remainder of 18.
The next digit of our result is 2. 
Result so far: 8311.2
The remainder is 18 after subtracting 162 from 180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Advancing to step 8:
The number 81 fits into 180 2 times, leaving a remainder of 18.
Write down 2 as next digit of the result. 
Result so far: 8311.22
If we take 162 away from 180, we end up with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

The final outcome is 8311.22, with a leftover of 0.018.