We look at the division of 644841 by 21 
The aim is to understand the frequency of 21 in 644841.

Let's proceed to step 1:
When dividing 6 by 21, we get 0 with a remainder of 6.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtracting 0 from 6 leaves us with 6.
Take the next digit (4) from the dividend and append it to 6, then repeat: 64 / 21

Moving on to step 2:
When dividing 64 by 21, we get 3 with a remainder of 1.
Put 3 as the next digit of the answer. 
Result so far: 3.0
If we subtract 63 from 64, we get 1.
Include the next digit (4) from the dividend after 1, then repeat: 14 / 21

Going ahead to step 3:
21 goes into 14 0 times with a remainder of 14.
Record the quotient 0 as the next digit in the result. 
Result so far: 30.0
If we take 0 away from 14, we end up with 14.
Bring next digit (8) of the dividend behind the 14 and repeat the process: 148 / 21

Advancing to step 4:
When dividing 148 by 21, we get 7 with a remainder of 1.
Write down 7 as next digit of the result. 
Result so far: 307.0
Subtracting 147 from 148 leaves us with 1.
Grab the next digit (4) from the dividend, add it to 1, then carry on: 14 / 21

Advancing to step 5:
21 goes into 14 0 times with a remainder of 14.
Put 0 as the next digit of the answer. 
Result so far: 3070.0
Deduct 0 from 14 and we're left with 14.
Take the next digit (1) from the dividend and append it to 14, then repeat: 141 / 21

Going ahead to step 6:
If we divide 141 by 21, we get 6 and a remainder of 15.
Record the quotient 6 as the next digit in the result. 
Result so far: 30706.0
If we subtract 126 from 141, 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.

Step 7:
The number 21 fits into 150 7 times, leaving a remainder of 3.
The next digit of our result is 7. 
Result so far: 30706.7
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.

Step 8:
When dividing 30 by 21, we get 1 with a remainder of 9.
Record the quotient 1 as the next digit in the result. 
Result so far: 30706.71
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:
90 divided by 21 is 4 with a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 30706.714
Subtracting 84 from 90 leaves us 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 10:
60 divided by 21 is 2 with a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 30706.7142
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.

On to step 11:
21 can be fit into 180 8 times, resulting in a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 30706.71428
Subtracting 168 from 180 leaves us 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.

Advancing to step 12:
If we divide 120 by 21, we get 5 and a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 30706.714285
If we subtract 105 from 120, 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.

Going ahead 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: 30706.7142857
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.

Going ahead to step 14:
21 can be fit into 30 1 times, resulting in a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 30706.71428571
The remainder is 9 after subtracting 21 from 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

In conclusion, the division gives 30706.71428571 with a balance of 9e-09.