We're dividing 604920 by 21 
The aim is to understand the frequency of 21 in 604920.

Moving on 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
Deduct 0 from 6 and we're left with 6.
Take the next digit (0) from the dividend and append it to 6, then repeat: 60 / 21

Moving on to step 2:
When dividing 60 by 21, we get 2 with a remainder of 18.
Use 2 as the next digit of our solution. 
Result so far: 2.0
Subtract 42 from 60 to get 18.
Append the next digit (4) from the dividend to 18 and continue with: 184 / 21

Let's proceed to step 3:
21 can be fit into 184 8 times, resulting in a remainder of 16.
Use 8 as the next digit of our solution. 
Result so far: 28.0
Subtract 168 from 184 to get 16.
Append the next digit (9) from the dividend to 16 and continue with: 169 / 21

Moving on to step 4:
21 can be fit into 169 8 times, resulting in a remainder of 1.
The next digit of our result is 8. 
Result so far: 288.0
If we subtract 168 from 169, we get 1.
Include the next digit (2) from the dividend after 1, then repeat: 12 / 21

Step 5:
If we divide 12 by 21, we get 0 and a remainder of 12.
Use 0 as the next digit of our solution. 
Result so far: 2880.0
If we subtract 0 from 12, we get 12.
Include the next digit (0) from the dividend after 12, then repeat: 120 / 21

On to step 6:
If we divide 120 by 21, we get 5 and a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 28805.0
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.

Step 7:
The number 21 fits into 150 7 times, leaving a remainder of 3.
Use 7 as the next digit of our solution. 
Result so far: 28805.7
If we take 147 away from 150, we end up 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.

Advancing to step 8:
30 divided by 21 is 1 with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 28805.71
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.

On to step 9:
The number 21 fits into 90 4 times, leaving a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 28805.714
Deduct 84 from 90 and we're left 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 10:
If we divide 60 by 21, we get 2 and a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 28805.7142
The remainder is 18 after subtracting 42 from 60.
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 next digit of our result is 8. 
Result so far: 28805.71428
If we take 168 away from 180, we end up 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:
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: 28805.714285
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.

Going ahead to step 13:
21 goes into 150 7 times with a remainder of 3.
Use 7 as the next digit of our solution. 
Result so far: 28805.7142857
Deduct 147 from 150 and we're left 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:
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: 28805.71428571
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.

The final outcome is 28805.71428571, with a leftover of 9e-09.