223869 ÷ 21 
The aim is to understand the frequency of 21 in 223869.

Let's proceed to step 1:
2 divided by 21 is 0 with a remainder of 2.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 2 and we're left with 2.
Grab the next digit (2) from the dividend, add it to 2, then carry on: 22 / 21

Step 2:
21 can be fit into 22 1 times, resulting in a remainder of 1.
Write down 1 as next digit of the result. 
Result so far: 1.0
Subtract 21 from 22 to get 1.
Grab the next digit (3) from the dividend, add it to 1, then carry on: 13 / 21

Moving on to step 3:
13 divided by 21 is 0 with a remainder of 13.
The number 0 becomes the next digit in our result. 
Result so far: 10.0
The remainder is 13 after subtracting 0 from 13.
Include the next digit (8) from the dividend after 13, then repeat: 138 / 21

On to step 4:
The number 21 fits into 138 6 times, leaving a remainder of 12.
Put 6 as the next digit of the answer. 
Result so far: 106.0
Deduct 126 from 138 and we're left with 12.
Grab the next digit (6) from the dividend, add it to 12, then carry on: 126 / 21

On to step 5:
21 goes into 126 6 times with a remainder of 0.
Use 6 as the next digit of our solution. 
Result so far: 1066.0
The remainder is 0 after subtracting 126 from 126.
Append the next digit (9) from the dividend to 0 and continue with: 9 / 21

Let's proceed to step 6:
21 can be fit into 9 0 times, resulting in a remainder of 9.
The next digit of our result is 0. 
Result so far: 10660.0
If we subtract 0 from 9, we get 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 7:
21 goes into 90 4 times with a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 10660.4
If we take 84 away from 90, 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.

Moving on to step 8:
60 divided by 21 is 2 with a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 10660.42
Subtracting 42 from 60 leaves us 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.

Moving on to step 9:
180 divided by 21 is 8 with a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 10660.428
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.

Step 10:
When dividing 120 by 21, we get 5 with a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 10660.4285
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.

On to step 11:
21 can be fit into 150 7 times, resulting in a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 10660.42857
If we subtract 147 from 150, we get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Moving on to step 12:
The number 21 fits into 30 1 times, leaving a remainder of 9.
Record the quotient 1 as the next digit in the result. 
Result so far: 10660.428571
If we subtract 21 from 30, we get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Let's proceed to step 13:
The number 21 fits into 90 4 times, leaving a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 10660.4285714
If we take 84 away from 90, 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 14:
The number 21 fits into 60 2 times, leaving a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 10660.42857142
Subtracting 42 from 60 leaves us 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.

The final result is 10660.42857142 with a remainder of 1.8e-08.