821154 ÷ 21 
The aim is to understand the frequency of 21 in 821154.

Step 1:
When dividing 8 by 21, we get 0 with a remainder of 8.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 8 and we're left with 8.
Grab the next digit (2) from the dividend, add it to 8, then carry on: 82 / 21

Step 2:
21 can be fit into 82 3 times, resulting in a remainder of 19.
Use 3 as the next digit of our solution. 
Result so far: 3.0
Deduct 63 from 82 and we're left with 19.
Fetch the next digit (1) from the dividend, attach it to 19 and continue: 191 / 21

Moving on to step 3:
The number 21 fits into 191 9 times, leaving a remainder of 2.
Use 9 as the next digit of our solution. 
Result so far: 39.0
If we subtract 189 from 191, we get 2.
Fetch the next digit (1) from the dividend, attach it to 2 and continue: 21 / 21

Advancing to step 4:
If we divide 21 by 21, we get 1 and a remainder of 0.
The number 1 becomes the next digit in our result. 
Result so far: 391.0
The remainder is 0 after subtracting 21 from 21.
Grab the next digit (5) from the dividend, add it to 0, then carry on: 5 / 21

Moving on to step 5:
If we divide 5 by 21, we get 0 and a remainder of 5.
Record the quotient 0 as the next digit in the result. 
Result so far: 3910.0
Subtracting 0 from 5 leaves us with 5.
Append the next digit (4) from the dividend to 5 and continue with: 54 / 21

Going ahead to step 6:
The number 21 fits into 54 2 times, leaving a remainder of 12.
Use 2 as the next digit of our solution. 
Result so far: 39102.0
If we subtract 42 from 54, 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.

Step 7:
21 goes into 120 5 times with a remainder of 15.
Use 5 as the next digit of our solution. 
Result so far: 39102.5
Subtract 105 from 120 to get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Let's proceed to step 8:
21 goes into 150 7 times with a remainder of 3.
Use 7 as the next digit of our solution. 
Result so far: 39102.57
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.

Going ahead to step 9:
The number 21 fits into 30 1 times, leaving a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 39102.571
Deduct 21 from 30 and we're left 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.

Moving on to step 10:
90 divided by 21 is 4 with a remainder of 6.
The next digit of our result is 4. 
Result so far: 39102.5714
Deduct 84 from 90 and we're left 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.

Let's proceed to step 11:
If we divide 60 by 21, we get 2 and a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 39102.57142
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.

Going ahead to step 12:
21 goes into 180 8 times with a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 39102.571428
The remainder is 12 after subtracting 168 from 180.
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 13:
The number 21 fits into 120 5 times, leaving a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 39102.5714285
If we take 105 away from 120, we end up with 15.
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 14:
21 goes into 150 7 times with a remainder of 3.
Use 7 as the next digit of our solution. 
Result so far: 39102.57142857
Subtracting 147 from 150 leaves us with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

The final outcome is 39102.57142857, with a leftover of 3e-09.