We look at the division of 480735 by 21 
The aim is to understand the frequency of 21 in 480735.

Advancing to step 1:
When dividing 4 by 21, we get 0 with a remainder of 4.
The next digit of our result is 0. 
Result so far: 0.0
If we subtract 0 from 4, we get 4.
Grab the next digit (8) from the dividend, add it to 4, then carry on: 48 / 21

Advancing to step 2:
21 can be fit into 48 2 times, resulting in a remainder of 6.
The next digit of our result is 2. 
Result so far: 2.0
Deduct 42 from 48 and we're left with 6.
Append the next digit (0) from the dividend to 6 and continue with: 60 / 21

Going ahead to step 3:
The number 21 fits into 60 2 times, leaving a remainder of 18.
The next digit of our result is 2. 
Result so far: 22.0
Deduct 42 from 60 and we're left with 18.
Append the next digit (7) from the dividend to 18 and continue with: 187 / 21

Advancing to step 4:
The number 21 fits into 187 8 times, leaving a remainder of 19.
Put 8 as the next digit of the answer. 
Result so far: 228.0
Subtract 168 from 187 to get 19.
Fetch the next digit (3) from the dividend, attach it to 19 and continue: 193 / 21

Step 5:
21 goes into 193 9 times with a remainder of 4.
Put 9 as the next digit of the answer. 
Result so far: 2289.0
If we subtract 189 from 193, we get 4.
Bring next digit (5) of the dividend behind the 4 and repeat the process: 45 / 21

Step 6:
21 goes into 45 2 times with a remainder of 3.
The number 2 becomes the next digit in our result. 
Result so far: 22892.0
The remainder is 3 after subtracting 42 from 45.
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 7:
The number 21 fits into 30 1 times, leaving a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 22892.1
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.

On to step 8:
The number 21 fits into 90 4 times, leaving a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 22892.14
Subtract 84 from 90 to get 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

On to step 9:
21 goes into 60 2 times with a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 22892.142
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.

Let's proceed to step 10:
180 divided by 21 is 8 with a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 22892.1428
Deduct 168 from 180 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.

Advancing to step 11:
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: 22892.14285
Subtract 105 from 120 to 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 12:
The number 21 fits into 150 7 times, leaving a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 22892.142857
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.

Step 13:
When dividing 30 by 21, we get 1 with a remainder of 9.
Put 1 as the next digit of the answer. 
Result so far: 22892.1428571
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.

Step 14:
90 divided by 21 is 4 with a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 22892.14285714
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.

The final outcome is 22892.14285714, with a leftover of 6e-09.