We're dividing 43963183 by 21 
The aim is to understand the frequency of 21 in 43963183.

On to step 1:
If we divide 4 by 21, we get 0 and a remainder of 4.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we subtract 0 from 4, we get 4.
Append the next digit (3) from the dividend to 4 and continue with: 43 / 21

Going ahead to step 2:
21 can be fit into 43 2 times, resulting in a remainder of 1.
The number 2 becomes the next digit in our result. 
Result so far: 2.0
Subtract 42 from 43 to get 1.
Grab the next digit (9) from the dividend, add it to 1, then carry on: 19 / 21

Moving on to step 3:
21 can be fit into 19 0 times, resulting in a remainder of 19.
Write down 0 as next digit of the result. 
Result so far: 20.0
Deduct 0 from 19 and we're left with 19.
Include the next digit (6) from the dividend after 19, then repeat: 196 / 21

Moving on to step 4:
196 divided by 21 is 9 with a remainder of 7.
The number 9 becomes the next digit in our result. 
Result so far: 209.0
If we subtract 189 from 196, we get 7.
Append the next digit (3) from the dividend to 7 and continue with: 73 / 21

Moving on to step 5:
21 can be fit into 73 3 times, resulting in a remainder of 10.
Put 3 as the next digit of the answer. 
Result so far: 2093.0
The remainder is 10 after subtracting 63 from 73.
Fetch the next digit (1) from the dividend, attach it to 10 and continue: 101 / 21

On to step 6:
The number 21 fits into 101 4 times, leaving a remainder of 17.
The number 4 becomes the next digit in our result. 
Result so far: 20934.0
Subtract 84 from 101 to get 17.
Take the next digit (8) from the dividend and append it to 17, then repeat: 178 / 21

Moving on to step 7:
21 can be fit into 178 8 times, resulting in a remainder of 10.
The next digit of our result is 8. 
Result so far: 209348.0
Deduct 168 from 178 and we're left with 10.
Take the next digit (3) from the dividend and append it to 10, then repeat: 103 / 21

Let's proceed to step 8:
If we divide 103 by 21, we get 4 and a remainder of 19.
Put 4 as the next digit of the answer. 
Result so far: 2093484.0
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.

Advancing to step 9:
190 divided by 21 is 9 with a remainder of 1.
Put 9 as the next digit of the answer. 
Result so far: 2093484.9
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.

Step 10:
21 can be fit into 10 0 times, resulting in a remainder of 10.
Write down 0 as next digit of the result. 
Result so far: 2093484.9
If we take 0 away from 10, we end up 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.

On to step 11:
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: 2093484.904
Subtract 84 from 100 to 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.

On to step 12:
The number 21 fits into 160 7 times, leaving a remainder of 13.
Use 7 as the next digit of our solution. 
Result so far: 2093484.9047
Deduct 147 from 160 and we're left with 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 13:
The number 21 fits into 130 6 times, leaving a remainder of 4.
The number 6 becomes the next digit in our result. 
Result so far: 2093484.90476
If we subtract 126 from 130, 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.

Moving on to step 14:
The number 21 fits into 40 1 times, leaving a remainder of 19.
Put 1 as the next digit of the answer. 
Result so far: 2093484.904761
The remainder is 19 after subtracting 21 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

On to step 15:
The number 21 fits into 190 9 times, leaving a remainder of 1.
Record the quotient 9 as the next digit in the result. 
Result so far: 2093484.9047619
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.

Let's proceed to step 16:
10 divided by 21 is 0 with a remainder of 10.
The number 0 becomes the next digit in our result. 
Result so far: 2093484.9047619
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.

Our division results in 2093484.9047619 with a remaining 1e-08.