621867 ÷ 21 
The aim is to understand the frequency of 21 in 621867.

Advancing to step 1:
6 divided by 21 is 0 with a remainder of 6.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we subtract 0 from 6, we get 6.
Include the next digit (2) from the dividend after 6, then repeat: 62 / 21

Let's proceed to step 2:
When dividing 62 by 21, we get 2 with a remainder of 20.
Record the quotient 2 as the next digit in the result. 
Result so far: 2.0
Subtract 42 from 62 to get 20.
Include the next digit (1) from the dividend after 20, then repeat: 201 / 21

Moving on to step 3:
When dividing 201 by 21, we get 9 with a remainder of 12.
Record the quotient 9 as the next digit in the result. 
Result so far: 29.0
The remainder is 12 after subtracting 189 from 201.
Include the next digit (8) from the dividend after 12, then repeat: 128 / 21

On to step 4:
128 divided by 21 is 6 with a remainder of 2.
Record the quotient 6 as the next digit in the result. 
Result so far: 296.0
If we take 126 away from 128, we end up with 2.
Include the next digit (6) from the dividend after 2, then repeat: 26 / 21

Moving on to step 5:
The number 21 fits into 26 1 times, leaving a remainder of 5.
The number 1 becomes the next digit in our result. 
Result so far: 2961.0
If we take 21 away from 26, we end up with 5.
Append the next digit (7) from the dividend to 5 and continue with: 57 / 21

Let's proceed to step 6:
57 divided by 21 is 2 with a remainder of 15.
The next digit of our result is 2. 
Result so far: 29612.0
If we subtract 42 from 57, we 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.

Moving on to step 7:
When dividing 150 by 21, we get 7 with a remainder of 3.
The next digit of our result is 7. 
Result so far: 29612.7
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.

Going ahead to step 8:
If we divide 30 by 21, we get 1 and a remainder of 9.
Put 1 as the next digit of the answer. 
Result so far: 29612.71
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.

Step 9:
21 goes into 90 4 times with a remainder of 6.
Write down 4 as next digit of the result. 
Result so far: 29612.714
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.

Moving on to step 10:
21 goes into 60 2 times with a remainder of 18.
Use 2 as the next digit of our solution. 
Result so far: 29612.7142
Subtract 42 from 60 to get 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 11:
The number 21 fits into 180 8 times, leaving a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 29612.71428
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.

Step 12:
The number 21 fits into 120 5 times, leaving a remainder of 15.
Write down 5 as next digit of the result. 
Result so far: 29612.714285
Subtracting 105 from 120 leaves us 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.

Let's proceed to step 13:
150 divided by 21 is 7 with a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 29612.7142857
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.

Moving on to step 14:
21 can be fit into 30 1 times, resulting in a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 29612.71428571
If we take 21 away from 30, we end up 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.

After the division, we end up with 29612.71428571 and a remainder of 9e-09.