We look at the division of 252347 by 21 
The aim is to understand the frequency of 21 in 252347.

On to step 1:
If we divide 2 by 21, we get 0 and a remainder of 2.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 2, we end up with 2.
Grab the next digit (5) from the dividend, add it to 2, then carry on: 25 / 21

Step 2:
21 can be fit into 25 1 times, resulting in a remainder of 4.
Put 1 as the next digit of the answer. 
Result so far: 1.0
If we take 21 away from 25, we end up with 4.
Take the next digit (2) from the dividend and append it to 4, then repeat: 42 / 21

Let's proceed to step 3:
42 divided by 21 is 2 with a remainder of 0.
Record the quotient 2 as the next digit in the result. 
Result so far: 12.0
Deduct 42 from 42 and we're left with 0.
Bring next digit (3) of the dividend behind the 0 and repeat the process: 3 / 21

Step 4:
If we divide 3 by 21, we get 0 and a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 120.0
The remainder is 3 after subtracting 0 from 3.
Take the next digit (4) from the dividend and append it to 3, then repeat: 34 / 21

Advancing to step 5:
If we divide 34 by 21, we get 1 and a remainder of 13.
Put 1 as the next digit of the answer. 
Result so far: 1201.0
Subtracting 21 from 34 leaves us with 13.
Append the next digit (7) from the dividend to 13 and continue with: 137 / 21

On to step 6:
21 goes into 137 6 times with a remainder of 11.
Write down 6 as next digit of the result. 
Result so far: 12016.0
The remainder is 11 after subtracting 126 from 137.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Let's proceed to step 7:
If we divide 110 by 21, we get 5 and a remainder of 5.
The number 5 becomes the next digit in our result. 
Result so far: 12016.5
Deduct 105 from 110 and we're left with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Advancing to step 8:
If we divide 50 by 21, we get 2 and a remainder of 8.
Use 2 as the next digit of our solution. 
Result so far: 12016.52
If we subtract 42 from 50, we get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Step 9:
21 can be fit into 80 3 times, resulting in a remainder of 17.
The next digit of our result is 3. 
Result so far: 12016.523
Deduct 63 from 80 and we're left with 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

On to step 10:
The number 21 fits into 170 8 times, leaving a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 12016.5238
Subtracting 168 from 170 leaves us with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Moving on to step 11:
20 divided by 21 is 0 with a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 12016.5238
Subtracting 0 from 20 leaves us with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Let's proceed to step 12:
200 divided by 21 is 9 with a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 12016.523809
The remainder is 11 after subtracting 189 from 200.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Step 13:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Put 5 as the next digit of the answer. 
Result so far: 12016.5238095
The remainder is 5 after subtracting 105 from 110.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Going ahead to step 14:
If we divide 50 by 21, we get 2 and a remainder of 8.
Write down 2 as next digit of the result. 
Result so far: 12016.52380952
Subtract 42 from 50 to get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

The final result is 12016.52380952 with a remainder of 8e-09.