We look at the division of 851112 by 21 
The aim is to understand the frequency of 21 in 851112.

Going ahead to step 1:
When dividing 8 by 21, we get 0 with a remainder of 8.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtracting 0 from 8 leaves us with 8.
Append the next digit (5) from the dividend to 8 and continue with: 85 / 21

On to step 2:
When dividing 85 by 21, we get 4 with a remainder of 1.
Record the quotient 4 as the next digit in the result. 
Result so far: 4.0
Subtracting 84 from 85 leaves us with 1.
Bring next digit (1) of the dividend behind the 1 and repeat the process: 11 / 21

On to step 3:
21 can be fit into 11 0 times, resulting in a remainder of 11.
The number 0 becomes the next digit in our result. 
Result so far: 40.0
Subtract 0 from 11 to get 11.
Take the next digit (1) from the dividend and append it to 11, then repeat: 111 / 21

Let's proceed to step 4:
If we divide 111 by 21, we get 5 and a remainder of 6.
The next digit of our result is 5. 
Result so far: 405.0
If we take 105 away from 111, we end up with 6.
Take the next digit (1) from the dividend and append it to 6, then repeat: 61 / 21

Step 5:
21 goes into 61 2 times with a remainder of 19.
Record the quotient 2 as the next digit in the result. 
Result so far: 4052.0
If we take 42 away from 61, we end up with 19.
Take the next digit (2) from the dividend and append it to 19, then repeat: 192 / 21

Let's proceed to step 6:
If we divide 192 by 21, we get 9 and a remainder of 3.
The next digit of our result is 9. 
Result so far: 40529.0
Subtract 189 from 192 to get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 7:
The number 21 fits into 30 1 times, leaving a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 40529.1
The remainder is 9 after subtracting 21 from 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Advancing to step 8:
21 can be fit into 90 4 times, resulting in a remainder of 6.
Write down 4 as next digit of the result. 
Result so far: 40529.14
Subtract 84 from 90 to get 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

On to step 9:
21 goes into 60 2 times with a remainder of 18.
Write down 2 as next digit of the result. 
Result so far: 40529.142
Subtracting 42 from 60 leaves us 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.

Let's proceed to step 10:
21 goes into 180 8 times with a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 40529.1428
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.

Let's proceed to step 11:
120 divided by 21 is 5 with a remainder of 15.
Write down 5 as next digit of the result. 
Result so far: 40529.14285
The remainder is 15 after subtracting 105 from 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

On to step 12:
21 goes into 150 7 times with a remainder of 3.
Use 7 as the next digit of our solution. 
Result so far: 40529.142857
If we subtract 147 from 150, we get 3.
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:
The number 21 fits into 30 1 times, leaving a remainder of 9.
Record the quotient 1 as the next digit in the result. 
Result so far: 40529.1428571
Deduct 21 from 30 and we're left 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:
When dividing 90 by 21, we get 4 with a remainder of 6.
The next digit of our result is 4. 
Result so far: 40529.14285714
If we take 84 away from 90, 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.

After the division, we end up with 40529.14285714 and a remainder of 6e-09.