We divide 520107 by 21
The aim is to understand the frequency of 21 in 520107.

Moving on to step 1:
When dividing 5 by 21, we get 0 with a remainder of 5.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 5 to get 5.
Fetch the next digit (2) from the dividend, attach it to 5 and continue: 52 / 21

Going ahead to step 2:
When dividing 52 by 21, we get 2 with a remainder of 10.
Write down 2 as next digit of the result. 
Result so far: 2.0
If we subtract 42 from 52, we get 10.
Fetch the next digit (0) from the dividend, attach it to 10 and continue: 100 / 21

On to step 3:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 24.0
Subtracting 84 from 100 leaves us with 16.
Include the next digit (1) from the dividend after 16, then repeat: 161 / 21

Let's proceed to step 4:
The number 21 fits into 161 7 times, leaving a remainder of 14.
Record the quotient 7 as the next digit in the result. 
Result so far: 247.0
The remainder is 14 after subtracting 147 from 161.
Include the next digit (0) from the dividend after 14, then repeat: 140 / 21

Going ahead to step 5:
21 goes into 140 6 times with a remainder of 14.
Put 6 as the next digit of the answer. 
Result so far: 2476.0
Subtract 126 from 140 to get 14.
Take the next digit (7) from the dividend and append it to 14, then repeat: 147 / 21

On to step 6:
147 divided by 21 is 7 with a remainder of 0.
Use 7 as the next digit of our solution. 
Result so far: 24767.0
Subtracting 147 from 147 leaves us with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Advancing to step 7:
When dividing 0 by 21, we get 0 with a remainder of 0.
Record the quotient 0 as the next digit in the result. 
Result so far: 24767.0
If we subtract 0 from 0, we get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Let's proceed to step 8:
21 goes into 0 0 times with a remainder of 0.
Write down 0 as next digit of the result. 
Result so far: 24767.0
Subtract 0 from 0 to get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

The final outcome is 24767.0, with a leftover of 0.0.