We're dividing 518383 by 21 
The aim is to understand the frequency of 21 in 518383.

Step 1:
5 divided by 21 is 0 with a remainder of 5.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 5 and we're left with 5.
Fetch the next digit (1) from the dividend, attach it to 5 and continue: 51 / 21

Going ahead to step 2:
When dividing 51 by 21, we get 2 with a remainder of 9.
Put 2 as the next digit of the answer. 
Result so far: 2.0
Deduct 42 from 51 and we're left with 9.
Take the next digit (8) from the dividend and append it to 9, then repeat: 98 / 21

Moving on to step 3:
98 divided by 21 is 4 with a remainder of 14.
The number 4 becomes the next digit in our result. 
Result so far: 24.0
Deduct 84 from 98 and we're left with 14.
Bring next digit (3) of the dividend behind the 14 and repeat the process: 143 / 21

Advancing to step 4:
143 divided by 21 is 6 with a remainder of 17.
Put 6 as the next digit of the answer. 
Result so far: 246.0
Subtracting 126 from 143 leaves us with 17.
Include the next digit (8) from the dividend after 17, then repeat: 178 / 21

On to step 5:
178 divided by 21 is 8 with a remainder of 10.
Record the quotient 8 as the next digit in the result. 
Result so far: 2468.0
Deduct 168 from 178 and we're left with 10.
Bring next digit (3) of the dividend behind the 10 and repeat the process: 103 / 21

Let's proceed to step 6:
When dividing 103 by 21, we get 4 with a remainder of 19.
Use 4 as the next digit of our solution. 
Result so far: 24684.0
Subtracting 84 from 103 leaves us with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Let's proceed to step 7:
21 can be fit into 190 9 times, resulting in a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 24684.9
Subtracting 189 from 190 leaves us 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.

Moving on to step 8:
21 can be fit into 10 0 times, resulting in a remainder of 10.
The number 0 becomes the next digit in our result. 
Result so far: 24684.9
The remainder is 10 after subtracting 0 from 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Let's proceed to step 9:
When dividing 100 by 21, we get 4 with a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 24684.904
If we subtract 84 from 100, we get 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Let's proceed to step 10:
If we divide 160 by 21, we get 7 and a remainder of 13.
Use 7 as the next digit of our solution. 
Result so far: 24684.9047
If we subtract 147 from 160, we get 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

On to step 11:
If we divide 130 by 21, we get 6 and a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 24684.90476
Subtracting 126 from 130 leaves us with 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:
When dividing 40 by 21, we get 1 with a remainder of 19.
Put 1 as the next digit of the answer. 
Result so far: 24684.904761
If we subtract 21 from 40, we 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.

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: 24684.9047619
If we subtract 189 from 190, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Let's proceed to step 14:
21 can be fit into 10 0 times, resulting in a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 24684.9047619
Subtracting 0 from 10 leaves us 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.

Our division results in 24684.9047619 with a remaining 1e-08.