We're dividing 12639196 by 21 
The aim is to understand the frequency of 21 in 12639196.

Step 1:
If we divide 1 by 21, we get 0 and a remainder of 1.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Deduct 0 from 1 and we're left with 1.
Append the next digit (2) from the dividend to 1 and continue with: 12 / 21

Moving on to step 2:
The number 21 fits into 12 0 times, leaving a remainder of 12.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtract 0 from 12 to get 12.
Append the next digit (6) from the dividend to 12 and continue with: 126 / 21

Going ahead to step 3:
If we divide 126 by 21, we get 6 and a remainder of 0.
Put 6 as the next digit of the answer. 
Result so far: 6.0
Subtract 126 from 126 to get 0.
Grab the next digit (3) from the dividend, add it to 0, then carry on: 3 / 21

Let's proceed to step 4:
21 can be fit into 3 0 times, resulting in a remainder of 3.
The number 0 becomes the next digit in our result. 
Result so far: 60.0
Deduct 0 from 3 and we're left with 3.
Append the next digit (9) from the dividend to 3 and continue with: 39 / 21

On to step 5:
When dividing 39 by 21, we get 1 with a remainder of 18.
The number 1 becomes the next digit in our result. 
Result so far: 601.0
If we subtract 21 from 39, we get 18.
Bring next digit (1) of the dividend behind the 18 and repeat the process: 181 / 21

Moving on to step 6:
21 goes into 181 8 times with a remainder of 13.
The number 8 becomes the next digit in our result. 
Result so far: 6018.0
If we take 168 away from 181, we end up with 13.
Bring next digit (9) of the dividend behind the 13 and repeat the process: 139 / 21

Moving on to step 7:
The number 21 fits into 139 6 times, leaving a remainder of 13.
Use 6 as the next digit of our solution. 
Result so far: 60186.0
Subtract 126 from 139 to get 13.
Grab the next digit (6) from the dividend, add it to 13, then carry on: 136 / 21

Let's proceed to step 8:
21 can be fit into 136 6 times, resulting in a remainder of 10.
The next digit of our result is 6. 
Result so far: 601866.0
If we take 126 away from 136, 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.

Let's proceed to step 9:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 601866.4
If we take 84 away from 100, we end up with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Advancing to step 10:
21 goes into 160 7 times with a remainder of 13.
The next digit of our result is 7. 
Result so far: 601866.47
The remainder is 13 after subtracting 147 from 160.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

On to step 11:
130 divided by 21 is 6 with a remainder of 4.
Use 6 as the next digit of our solution. 
Result so far: 601866.476
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.

Step 12:
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: 601866.4761
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.

Step 13:
When dividing 190 by 21, we get 9 with a remainder of 1.
Write down 9 as next digit of the result. 
Result so far: 601866.47619
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.

Advancing to step 14:
21 goes into 10 0 times with a remainder of 10.
Write down 0 as next digit of the result. 
Result so far: 601866.47619
Deduct 0 from 10 and we're left 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.

Advancing to step 15:
If we divide 100 by 21, we get 4 and a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 601866.4761904
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.

Moving on to step 16:
The number 21 fits into 160 7 times, leaving a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 601866.47619047
Subtracting 147 from 160 leaves us 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.

The final result is 601866.47619047 with a remainder of 1.3e-08.