We look at the division of 952399 by 21 
The aim is to understand the frequency of 21 in 952399.

On to step 1:
The number 21 fits into 9 0 times, leaving a remainder of 9.
Put 0 as the next digit of the answer. 
Result so far: 0.0
The remainder is 9 after subtracting 0 from 9.
Take the next digit (5) from the dividend and append it to 9, then repeat: 95 / 21

Going ahead to step 2:
When dividing 95 by 21, we get 4 with a remainder of 11.
The number 4 becomes the next digit in our result. 
Result so far: 4.0
Subtract 84 from 95 to get 11.
Fetch the next digit (2) from the dividend, attach it to 11 and continue: 112 / 21

Step 3:
21 goes into 112 5 times with a remainder of 7.
Write down 5 as next digit of the result. 
Result so far: 45.0
Subtract 105 from 112 to get 7.
Append the next digit (3) from the dividend to 7 and continue with: 73 / 21

Moving on to step 4:
21 goes into 73 3 times with a remainder of 10.
The number 3 becomes the next digit in our result. 
Result so far: 453.0
Deduct 63 from 73 and we're left with 10.
Append the next digit (9) from the dividend to 10 and continue with: 109 / 21

On to step 5:
109 divided by 21 is 5 with a remainder of 4.
The next digit of our result is 5. 
Result so far: 4535.0
If we take 105 away from 109, we end up with 4.
Fetch the next digit (9) from the dividend, attach it to 4 and continue: 49 / 21

Going ahead to step 6:
The number 21 fits into 49 2 times, leaving a remainder of 7.
The number 2 becomes the next digit in our result. 
Result so far: 45352.0
If we subtract 42 from 49, 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 7:
When dividing 70 by 21, we get 3 with a remainder of 7.
The next digit of our result is 3. 
Result so far: 45352.3
Subtracting 63 from 70 leaves us with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Going ahead to step 8:
21 goes into 70 3 times with a remainder of 7.
The number 3 becomes the next digit in our result. 
Result so far: 45352.33
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.

The final outcome is 45352.33, with a leftover of 0.007.