Let's divide 970821 by 21
The aim is to understand the frequency of 21 in 970821.

Step 1:
21 can be fit into 9 0 times, resulting in a remainder of 9.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we take 0 away from 9, we end up with 9.
Take the next digit (7) from the dividend and append it to 9, then repeat: 97 / 21

Advancing to step 2:
21 can be fit into 97 4 times, resulting in a remainder of 13.
The number 4 becomes the next digit in our result. 
Result so far: 4.0
Deduct 84 from 97 and we're left with 13.
Include the next digit (0) from the dividend after 13, then repeat: 130 / 21

On to step 3:
21 can be fit into 130 6 times, resulting in a remainder of 4.
The next digit of our result is 6. 
Result so far: 46.0
Deduct 126 from 130 and we're left with 4.
Include the next digit (8) from the dividend after 4, then repeat: 48 / 21

Step 4:
If we divide 48 by 21, we get 2 and a remainder of 6.
Use 2 as the next digit of our solution. 
Result so far: 462.0
The remainder is 6 after subtracting 42 from 48.
Fetch the next digit (2) from the dividend, attach it to 6 and continue: 62 / 21

Going ahead to step 5:
62 divided by 21 is 2 with a remainder of 20.
Record the quotient 2 as the next digit in the result. 
Result so far: 4622.0
Subtracting 42 from 62 leaves us with 20.
Take the next digit (1) from the dividend and append it to 20, then repeat: 201 / 21

On to step 6:
21 goes into 201 9 times with a remainder of 12.
Put 9 as the next digit of the answer. 
Result so far: 46229.0
Deduct 189 from 201 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.

Moving on to step 7:
When dividing 120 by 21, we get 5 with a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 46229.5
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.

On to step 8:
When dividing 150 by 21, we get 7 with a remainder of 3.
The next digit of our result is 7. 
Result so far: 46229.57
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.

Going ahead to step 9:
When dividing 30 by 21, we get 1 with a remainder of 9.
The next digit of our result is 1. 
Result so far: 46229.571
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.

Let's proceed to step 10:
If we divide 90 by 21, we get 4 and a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 46229.5714
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.

Step 11:
The number 21 fits into 60 2 times, leaving a remainder of 18.
The next digit of our result is 2. 
Result so far: 46229.57142
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.

Going ahead to step 12:
The number 21 fits into 180 8 times, leaving a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 46229.571428
Subtract 168 from 180 to 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 13:
The number 21 fits into 120 5 times, leaving a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 46229.5714285
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.

Moving on to step 14:
The number 21 fits into 150 7 times, leaving a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 46229.57142857
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.

Our division results in 46229.57142857 with a remaining 3e-09.