We look at the division of 20321518 by 21 
The aim is to understand the frequency of 21 in 20321518.

Step 1:
2 divided by 21 is 0 with a remainder of 2.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 2, we end up with 2.
Grab the next digit (0) from the dividend, add it to 2, then carry on: 20 / 21

Advancing to step 2:
If we divide 20 by 21, we get 0 and a remainder of 20.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we subtract 0 from 20, we get 20.
Include the next digit (3) from the dividend after 20, then repeat: 203 / 21

Let's proceed to step 3:
21 goes into 203 9 times with a remainder of 14.
Use 9 as the next digit of our solution. 
Result so far: 9.0
Subtracting 189 from 203 leaves us with 14.
Include the next digit (2) from the dividend after 14, then repeat: 142 / 21

Going ahead to step 4:
21 goes into 142 6 times with a remainder of 16.
Record the quotient 6 as the next digit in the result. 
Result so far: 96.0
If we subtract 126 from 142, we get 16.
Fetch the next digit (1) from the dividend, attach it to 16 and continue: 161 / 21

Moving on to step 5:
The number 21 fits into 161 7 times, leaving a remainder of 14.
Put 7 as the next digit of the answer. 
Result so far: 967.0
Subtracting 147 from 161 leaves us with 14.
Include the next digit (5) from the dividend after 14, then repeat: 145 / 21

Going ahead to step 6:
When dividing 145 by 21, we get 6 with a remainder of 19.
The number 6 becomes the next digit in our result. 
Result so far: 9676.0
If we take 126 away from 145, we end up with 19.
Grab the next digit (1) from the dividend, add it to 19, then carry on: 191 / 21

Step 7:
21 can be fit into 191 9 times, resulting in a remainder of 2.
The next digit of our result is 9. 
Result so far: 96769.0
Subtracting 189 from 191 leaves us with 2.
Bring next digit (8) of the dividend behind the 2 and repeat the process: 28 / 21

Going ahead to step 8:
When dividing 28 by 21, we get 1 with a remainder of 7.
Record the quotient 1 as the next digit in the result. 
Result so far: 967691.0
If we subtract 21 from 28, we get 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Let's proceed to step 9:
21 can be fit into 70 3 times, resulting in a remainder of 7.
Record the quotient 3 as the next digit in the result. 
Result so far: 967691.3
Subtract 63 from 70 to get 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Let's proceed to step 10:
21 goes into 70 3 times with a remainder of 7.
The number 3 becomes the next digit in our result. 
Result so far: 967691.33
The remainder is 7 after subtracting 63 from 70.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

The quotient of the division is 967691.33, and the remainder is 0.007.