We look at the division of 435963 by 81 
The aim is to understand the frequency of 81 in 435963.

On to step 1:
The number 81 fits into 4 0 times, leaving a remainder of 4.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 4, we get 4.
Grab the next digit (3) from the dividend, add it to 4, then carry on: 43 / 81

Advancing to step 2:
When dividing 43 by 81, we get 0 with a remainder of 43.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 43 leaves us with 43.
Fetch the next digit (5) from the dividend, attach it to 43 and continue: 435 / 81

Advancing to step 3:
The number 81 fits into 435 5 times, leaving a remainder of 30.
Use 5 as the next digit of our solution. 
Result so far: 5.0
Subtracting 405 from 435 leaves us with 30.
Fetch the next digit (9) from the dividend, attach it to 30 and continue: 309 / 81

Going ahead to step 4:
309 divided by 81 is 3 with a remainder of 66.
Write down 3 as next digit of the result. 
Result so far: 53.0
If we take 243 away from 309, we end up with 66.
Take the next digit (6) from the dividend and append it to 66, then repeat: 666 / 81

Going ahead to step 5:
666 divided by 81 is 8 with a remainder of 18.
Use 8 as the next digit of our solution. 
Result so far: 538.0
The remainder is 18 after subtracting 648 from 666.
Include the next digit (3) from the dividend after 18, then repeat: 183 / 81

Step 6:
81 goes into 183 2 times with a remainder of 21.
Put 2 as the next digit of the answer. 
Result so far: 5382.0
Subtract 162 from 183 to get 21.
Since there are no more digits in the dividend, we add a zero to the remainder making it 210, and continue the process.

Step 7:
When dividing 210 by 81, we get 2 with a remainder of 48.
Record the quotient 2 as the next digit in the result. 
Result so far: 5382.2
Deduct 162 from 210 and we're left with 48.
Since there are no more digits in the dividend, we add a zero to the remainder making it 480, and continue the process.

Going ahead to step 8:
81 goes into 480 5 times with a remainder of 75.
The number 5 becomes the next digit in our result. 
Result so far: 5382.25
Subtract 405 from 480 to get 75.
Since there are no more digits in the dividend, we add a zero to the remainder making it 750, and continue the process.

Moving on to step 9:
750 divided by 81 is 9 with a remainder of 21.
The next digit of our result is 9. 
Result so far: 5382.259
If we subtract 729 from 750, we get 21.
Since there are no more digits in the dividend, we add a zero to the remainder making it 210, and continue the process.

Going ahead to step 10:
210 divided by 81 is 2 with a remainder of 48.
Write down 2 as next digit of the result. 
Result so far: 5382.2592
If we take 162 away from 210, we end up with 48.
Since there are no more digits in the dividend, we add a zero to the remainder making it 480, and continue the process.

Advancing to step 11:
If we divide 480 by 81, we get 5 and a remainder of 75.
The number 5 becomes the next digit in our result. 
Result so far: 5382.25925
If we subtract 405 from 480, we get 75.
Since there are no more digits in the dividend, we add a zero to the remainder making it 750, and continue the process.

Moving on to step 12:
If we divide 750 by 81, we get 9 and a remainder of 21.
Write down 9 as next digit of the result. 
Result so far: 5382.259259
If we subtract 729 from 750, we get 21.
Since there are no more digits in the dividend, we add a zero to the remainder making it 210, and continue the process.

Going ahead to step 13:
81 can be fit into 210 2 times, resulting in a remainder of 48.
Put 2 as the next digit of the answer. 
Result so far: 5382.2592592
Deduct 162 from 210 and we're left with 48.
Since there are no more digits in the dividend, we add a zero to the remainder making it 480, and continue the process.

Going ahead to step 14:
The number 81 fits into 480 5 times, leaving a remainder of 75.
Use 5 as the next digit of our solution. 
Result so far: 5382.25925925
The remainder is 75 after subtracting 405 from 480.
Since there are no more digits in the dividend, we add a zero to the remainder making it 750, and continue the process.

The final result is 5382.25925925 with a remainder of 7.5e-08.