We look at the division of 663760 by 81 
The aim is to understand the frequency of 81 in 663760.

On to step 1:
81 can be fit into 6 0 times, resulting in a remainder of 6.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 6 to get 6.
Bring next digit (6) of the dividend behind the 6 and repeat the process: 66 / 81

Going ahead to step 2:
81 goes into 66 0 times with a remainder of 66.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 66 and we're left with 66.
Take the next digit (3) from the dividend and append it to 66, then repeat: 663 / 81

On to step 3:
81 can be fit into 663 8 times, resulting in a remainder of 15.
The number 8 becomes the next digit in our result. 
Result so far: 8.0
Subtracting 648 from 663 leaves us with 15.
Append the next digit (7) from the dividend to 15 and continue with: 157 / 81

Let's proceed to step 4:
The number 81 fits into 157 1 times, leaving a remainder of 76.
The next digit of our result is 1. 
Result so far: 81.0
The remainder is 76 after subtracting 81 from 157.
Append the next digit (6) from the dividend to 76 and continue with: 766 / 81

Step 5:
When dividing 766 by 81, we get 9 with a remainder of 37.
The next digit of our result is 9. 
Result so far: 819.0
If we subtract 729 from 766, we get 37.
Append the next digit (0) from the dividend to 37 and continue with: 370 / 81

Advancing to step 6:
If we divide 370 by 81, we get 4 and a remainder of 46.
Use 4 as the next digit of our solution. 
Result so far: 8194.0
If we subtract 324 from 370, we get 46.
Since there are no more digits in the dividend, we add a zero to the remainder making it 460, and continue the process.

Going ahead to step 7:
81 can be fit into 460 5 times, resulting in a remainder of 55.
Write down 5 as next digit of the result. 
Result so far: 8194.5
If we take 405 away from 460, we end up with 55.
Since there are no more digits in the dividend, we add a zero to the remainder making it 550, and continue the process.

Step 8:
81 can be fit into 550 6 times, resulting in a remainder of 64.
The number 6 becomes the next digit in our result. 
Result so far: 8194.56
Subtracting 486 from 550 leaves us with 64.
Since there are no more digits in the dividend, we add a zero to the remainder making it 640, and continue the process.

Going ahead to step 9:
The number 81 fits into 640 7 times, leaving a remainder of 73.
Use 7 as the next digit of our solution. 
Result so far: 8194.567
If we take 567 away from 640, we end up with 73.
Since there are no more digits in the dividend, we add a zero to the remainder making it 730, and continue the process.

On to step 10:
730 divided by 81 is 9 with a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 8194.5679
If we subtract 729 from 730, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Moving on to step 11:
81 goes into 10 0 times with a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 8194.5679
The remainder is 10 after subtracting 0 from 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Advancing to step 12:
When dividing 100 by 81, we get 1 with a remainder of 19.
Write down 1 as next digit of the result. 
Result so far: 8194.567901
Subtract 81 from 100 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

On to step 13:
The number 81 fits into 190 2 times, leaving a remainder of 28.
Write down 2 as next digit of the result. 
Result so far: 8194.5679012
If we take 162 away from 190, we end up with 28.
Since there are no more digits in the dividend, we add a zero to the remainder making it 280, and continue the process.

Let's proceed to step 14:
If we divide 280 by 81, we get 3 and a remainder of 37.
The number 3 becomes the next digit in our result. 
Result so far: 8194.56790123
If we take 243 away from 280, we end up with 37.
Since there are no more digits in the dividend, we add a zero to the remainder making it 370, and continue the process.

The final outcome is 8194.56790123, with a leftover of 3.7e-08.