We're dividing 13912317 by 21 
The aim is to understand the frequency of 21 in 13912317.

Step 1:
If we divide 1 by 21, we get 0 and a remainder of 1.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 1 and we're left with 1.
Take the next digit (3) from the dividend and append it to 1, then repeat: 13 / 21

On to step 2:
The number 21 fits into 13 0 times, leaving a remainder of 13.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 13 to get 13.
Bring next digit (9) of the dividend behind the 13 and repeat the process: 139 / 21

On to step 3:
If we divide 139 by 21, we get 6 and a remainder of 13.
Use 6 as the next digit of our solution. 
Result so far: 6.0
Subtract 126 from 139 to get 13.
Fetch the next digit (1) from the dividend, attach it to 13 and continue: 131 / 21

Going ahead to step 4:
The number 21 fits into 131 6 times, leaving a remainder of 5.
The next digit of our result is 6. 
Result so far: 66.0
Deduct 126 from 131 and we're left with 5.
Take the next digit (2) from the dividend and append it to 5, then repeat: 52 / 21

Moving on to step 5:
21 can be fit into 52 2 times, resulting in a remainder of 10.
The next digit of our result is 2. 
Result so far: 662.0
The remainder is 10 after subtracting 42 from 52.
Take the next digit (3) from the dividend and append it to 10, then repeat: 103 / 21

Advancing to step 6:
103 divided by 21 is 4 with a remainder of 19.
The number 4 becomes the next digit in our result. 
Result so far: 6624.0
If we subtract 84 from 103, we get 19.
Include the next digit (1) from the dividend after 19, then repeat: 191 / 21

Going ahead to step 7:
If we divide 191 by 21, we get 9 and a remainder of 2.
The next digit of our result is 9. 
Result so far: 66249.0
Subtracting 189 from 191 leaves us with 2.
Append the next digit (7) from the dividend to 2 and continue with: 27 / 21

Moving on to step 8:
21 can be fit into 27 1 times, resulting in a remainder of 6.
Put 1 as the next digit of the answer. 
Result so far: 662491.0
If we take 21 away from 27, we end up with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Advancing to step 9:
The number 21 fits into 60 2 times, leaving a remainder of 18.
Put 2 as the next digit of the answer. 
Result so far: 662491.2
Subtract 42 from 60 to get 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Going ahead to step 10:
21 can be fit into 180 8 times, resulting in a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 662491.28
Subtract 168 from 180 to get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Moving on to step 11:
If we divide 120 by 21, we get 5 and a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 662491.285
Subtracting 105 from 120 leaves us with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Going ahead to step 12:
150 divided by 21 is 7 with a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 662491.2857
The remainder is 3 after subtracting 147 from 150.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Advancing to step 13:
30 divided by 21 is 1 with a remainder of 9.
The next digit of our result is 1. 
Result so far: 662491.28571
If we take 21 away from 30, we end up with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

On to step 14:
90 divided by 21 is 4 with a remainder of 6.
Write down 4 as next digit of the result. 
Result so far: 662491.285714
Deduct 84 from 90 and we're left with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Let's proceed to step 15:
21 goes into 60 2 times with a remainder of 18.
Put 2 as the next digit of the answer. 
Result so far: 662491.2857142
Deduct 42 from 60 and we're left with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Going ahead to step 16:
The number 21 fits into 180 8 times, leaving a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 662491.28571428
If we take 168 away from 180, we end up with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

The final result is 662491.28571428 with a remainder of 1.2e-08.