We look at the division of 83511578 by 81 
The aim is to understand the frequency of 81 in 83511578.

Moving on to step 1:
The number 81 fits into 8 0 times, leaving a remainder of 8.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
The remainder is 8 after subtracting 0 from 8.
Append the next digit (3) from the dividend to 8 and continue with: 83 / 81

On to step 2:
The number 81 fits into 83 1 times, leaving a remainder of 2.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
Subtracting 81 from 83 leaves us with 2.
Take the next digit (5) from the dividend and append it to 2, then repeat: 25 / 81

Advancing to step 3:
The number 81 fits into 25 0 times, leaving a remainder of 25.
The next digit of our result is 0. 
Result so far: 10.0
If we take 0 away from 25, we end up with 25.
Bring next digit (1) of the dividend behind the 25 and repeat the process: 251 / 81

Moving on to step 4:
81 goes into 251 3 times with a remainder of 8.
The number 3 becomes the next digit in our result. 
Result so far: 103.0
Subtracting 243 from 251 leaves us with 8.
Append the next digit (1) from the dividend to 8 and continue with: 81 / 81

On to step 5:
The number 81 fits into 81 1 times, leaving a remainder of 0.
The next digit of our result is 1. 
Result so far: 1031.0
Deduct 81 from 81 and we're left with 0.
Bring next digit (5) of the dividend behind the 0 and repeat the process: 5 / 81

Moving on to step 6:
81 goes into 5 0 times with a remainder of 5.
The number 0 becomes the next digit in our result. 
Result so far: 10310.0
The remainder is 5 after subtracting 0 from 5.
Take the next digit (7) from the dividend and append it to 5, then repeat: 57 / 81

Moving on to step 7:
81 can be fit into 57 0 times, resulting in a remainder of 57.
Write down 0 as next digit of the result. 
Result so far: 103100.0
If we subtract 0 from 57, we get 57.
Grab the next digit (8) from the dividend, add it to 57, then carry on: 578 / 81

Moving on to step 8:
81 goes into 578 7 times with a remainder of 11.
The number 7 becomes the next digit in our result. 
Result so far: 1031007.0
Subtracting 567 from 578 leaves us with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Step 9:
81 goes into 110 1 times with a remainder of 29.
The next digit of our result is 1. 
Result so far: 1031007.1
If we take 81 away from 110, we end up with 29.
Since there are no more digits in the dividend, we add a zero to the remainder making it 290, and continue the process.

Advancing to step 10:
81 goes into 290 3 times with a remainder of 47.
Write down 3 as next digit of the result. 
Result so far: 1031007.13
If we take 243 away from 290, we end up with 47.
Since there are no more digits in the dividend, we add a zero to the remainder making it 470, and continue the process.

On to step 11:
81 goes into 470 5 times with a remainder of 65.
The number 5 becomes the next digit in our result. 
Result so far: 1031007.135
Subtracting 405 from 470 leaves us with 65.
Since there are no more digits in the dividend, we add a zero to the remainder making it 650, and continue the process.

Moving on to step 12:
81 goes into 650 8 times with a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 1031007.1358
Deduct 648 from 650 and we're left with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

On to step 13:
81 goes into 20 0 times with a remainder of 20.
Record the quotient 0 as the next digit in the result. 
Result so far: 1031007.1358
If we subtract 0 from 20, we get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Going ahead to step 14:
81 can be fit into 200 2 times, resulting in a remainder of 38.
The next digit of our result is 2. 
Result so far: 1031007.135802
The remainder is 38 after subtracting 162 from 200.
Since there are no more digits in the dividend, we add a zero to the remainder making it 380, and continue the process.

Advancing to step 15:
When dividing 380 by 81, we get 4 with a remainder of 56.
Write down 4 as next digit of the result. 
Result so far: 1031007.1358024
If we take 324 away from 380, we end up with 56.
Since there are no more digits in the dividend, we add a zero to the remainder making it 560, and continue the process.

Step 16:
If we divide 560 by 81, we get 6 and a remainder of 74.
Record the quotient 6 as the next digit in the result. 
Result so far: 1031007.13580246
If we take 486 away from 560, we end up with 74.
Since there are no more digits in the dividend, we add a zero to the remainder making it 740, and continue the process.

The final result is 1031007.13580246 with a remainder of 7.4e-08.