We look at the division of 636199 by 21 
The aim is to understand the frequency of 21 in 636199.

Step 1:
6 divided by 21 is 0 with a remainder of 6.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we take 0 away from 6, we end up with 6.
Fetch the next digit (3) from the dividend, attach it to 6 and continue: 63 / 21

Step 2:
If we divide 63 by 21, we get 3 and a remainder of 0.
Record the quotient 3 as the next digit in the result. 
Result so far: 3.0
The remainder is 0 after subtracting 63 from 63.
Include the next digit (6) from the dividend after 0, then repeat: 6 / 21

Let's proceed to step 3:
21 goes into 6 0 times with a remainder of 6.
The next digit of our result is 0. 
Result so far: 30.0
If we subtract 0 from 6, we get 6.
Include the next digit (1) from the dividend after 6, then repeat: 61 / 21

Moving on to step 4:
61 divided by 21 is 2 with a remainder of 19.
The next digit of our result is 2. 
Result so far: 302.0
The remainder is 19 after subtracting 42 from 61.
Append the next digit (9) from the dividend to 19 and continue with: 199 / 21

On to step 5:
21 goes into 199 9 times with a remainder of 10.
Record the quotient 9 as the next digit in the result. 
Result so far: 3029.0
Deduct 189 from 199 and we're left with 10.
Take the next digit (9) from the dividend and append it to 10, then repeat: 109 / 21

Let's proceed to step 6:
109 divided by 21 is 5 with a remainder of 4.
The next digit of our result is 5. 
Result so far: 30295.0
If we subtract 105 from 109, we get 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Let's proceed to step 7:
The number 21 fits into 40 1 times, leaving a remainder of 19.
Use 1 as the next digit of our solution. 
Result so far: 30295.1
If we take 21 away from 40, we end up 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.

Advancing to step 8:
21 goes into 190 9 times with a remainder of 1.
Put 9 as the next digit of the answer. 
Result so far: 30295.19
If we take 189 away from 190, we end up 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.

On to step 9:
The number 21 fits into 10 0 times, leaving a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 30295.19
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.

Moving on to step 10:
The number 21 fits into 100 4 times, leaving a remainder of 16.
The next digit of our result is 4. 
Result so far: 30295.1904
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.

Step 11:
If we divide 160 by 21, we get 7 and a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 30295.19047
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.

Let's proceed to step 12:
If we divide 130 by 21, we get 6 and a remainder of 4.
Write down 6 as next digit of the result. 
Result so far: 30295.190476
If we take 126 away from 130, we end up 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.

Advancing to step 13:
21 goes into 40 1 times with a remainder of 19.
The number 1 becomes the next digit in our result. 
Result so far: 30295.1904761
Deduct 21 from 40 and we're left 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.

Step 14:
21 goes into 190 9 times with a remainder of 1.
Write down 9 as next digit of the result. 
Result so far: 30295.19047619
Deduct 189 from 190 and we're left 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.

The final result is 30295.19047619 with a remainder of 1e-09.