648331 ÷ 21 
The aim is to understand the frequency of 21 in 648331.

Moving on to step 1:
21 can be fit into 6 0 times, resulting in a remainder of 6.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtract 0 from 6 to get 6.
Append the next digit (4) from the dividend to 6 and continue with: 64 / 21

On to step 2:
21 goes into 64 3 times with a remainder of 1.
The number 3 becomes the next digit in our result. 
Result so far: 3.0
Subtract 63 from 64 to get 1.
Fetch the next digit (8) from the dividend, attach it to 1 and continue: 18 / 21

Moving on to step 3:
If we divide 18 by 21, we get 0 and a remainder of 18.
Record the quotient 0 as the next digit in the result. 
Result so far: 30.0
If we subtract 0 from 18, we get 18.
Fetch the next digit (3) from the dividend, attach it to 18 and continue: 183 / 21

Let's proceed to step 4:
If we divide 183 by 21, we get 8 and a remainder of 15.
Put 8 as the next digit of the answer. 
Result so far: 308.0
Subtract 168 from 183 to get 15.
Fetch the next digit (3) from the dividend, attach it to 15 and continue: 153 / 21

Going ahead to step 5:
21 can be fit into 153 7 times, resulting in a remainder of 6.
The number 7 becomes the next digit in our result. 
Result so far: 3087.0
If we subtract 147 from 153, we get 6.
Take the next digit (1) from the dividend and append it to 6, then repeat: 61 / 21

Advancing to step 6:
61 divided by 21 is 2 with a remainder of 19.
Write down 2 as next digit of the result. 
Result so far: 30872.0
Subtract 42 from 61 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Going ahead to step 7:
190 divided by 21 is 9 with a remainder of 1.
The next digit of our result is 9. 
Result so far: 30872.9
Deduct 189 from 190 and we're left with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

On to step 8:
10 divided by 21 is 0 with a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 30872.9
Subtract 0 from 10 to get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Going ahead to step 9:
21 goes into 100 4 times with a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 30872.904
If we take 84 away from 100, we end up with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

On to step 10:
21 goes into 160 7 times with a remainder of 13.
Write down 7 as next digit of the result. 
Result so far: 30872.9047
If we take 147 away from 160, we end up with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Moving on to step 11:
130 divided by 21 is 6 with a remainder of 4.
Write down 6 as next digit of the result. 
Result so far: 30872.90476
If we subtract 126 from 130, we get 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

On to step 12:
21 goes into 40 1 times with a remainder of 19.
Use 1 as the next digit of our solution. 
Result so far: 30872.904761
The remainder is 19 after subtracting 21 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

On to step 13:
21 can be fit into 190 9 times, resulting in a remainder of 1.
Write down 9 as next digit of the result. 
Result so far: 30872.9047619
If we take 189 away from 190, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Step 14:
If we divide 10 by 21, we get 0 and a remainder of 10.
Write down 0 as next digit of the result. 
Result so far: 30872.9047619
If we take 0 away from 10, we end up with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

The final result is 30872.9047619 with a remainder of 1e-08.