820161 divided by 21 
The aim is to understand the frequency of 21 in 820161.

Let's proceed to step 1:
21 goes into 8 0 times with a remainder of 8.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 8 and we're left with 8.
Bring next digit (2) of the dividend behind the 8 and repeat the process: 82 / 21

Step 2:
When dividing 82 by 21, we get 3 with a remainder of 19.
The number 3 becomes the next digit in our result. 
Result so far: 3.0
The remainder is 19 after subtracting 63 from 82.
Take the next digit (0) from the dividend and append it to 19, then repeat: 190 / 21

Going ahead to step 3:
The number 21 fits into 190 9 times, leaving a remainder of 1.
Record the quotient 9 as the next digit in the result. 
Result so far: 39.0
If we take 189 away from 190, we end up with 1.
Fetch the next digit (1) from the dividend, attach it to 1 and continue: 11 / 21

Step 4:
21 goes into 11 0 times with a remainder of 11.
The next digit of our result is 0. 
Result so far: 390.0
The remainder is 11 after subtracting 0 from 11.
Append the next digit (6) from the dividend to 11 and continue with: 116 / 21

Let's proceed to step 5:
When dividing 116 by 21, we get 5 with a remainder of 11.
Record the quotient 5 as the next digit in the result. 
Result so far: 3905.0
If we subtract 105 from 116, we get 11.
Append the next digit (1) from the dividend to 11 and continue with: 111 / 21

On to step 6:
111 divided by 21 is 5 with a remainder of 6.
Record the quotient 5 as the next digit in the result. 
Result so far: 39055.0
If we take 105 away from 111, we end up with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Going ahead to step 7:
21 goes into 60 2 times with a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 39055.2
If we take 42 away from 60, 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.

Step 8:
21 can be fit into 180 8 times, resulting in a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 39055.28
If we subtract 168 from 180, we get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Going ahead to step 9:
21 can be fit into 120 5 times, resulting in a remainder of 15.
The next digit of our result is 5. 
Result so far: 39055.285
The remainder is 15 after subtracting 105 from 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Going ahead to step 10:
21 goes into 150 7 times with a remainder of 3.
Use 7 as the next digit of our solution. 
Result so far: 39055.2857
The remainder is 3 after subtracting 147 from 150.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 11:
21 goes into 30 1 times with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 39055.28571
Subtracting 21 from 30 leaves us with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Going ahead to step 12:
The number 21 fits into 90 4 times, leaving a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 39055.285714
The remainder is 6 after subtracting 84 from 90.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Going ahead to step 13:
60 divided by 21 is 2 with a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 39055.2857142
Deduct 42 from 60 and we're left 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.

Step 14:
When dividing 180 by 21, we get 8 with a remainder of 12.
Put 8 as the next digit of the answer. 
Result so far: 39055.28571428
Deduct 168 from 180 and we're left with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

In conclusion, the division gives 39055.28571428 with a balance of 1.2e-08.