We're dividing 25307568 by 21 
The aim is to understand the frequency of 21 in 25307568.

On to step 1:
21 can be fit into 2 0 times, resulting in a remainder of 2.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtracting 0 from 2 leaves us with 2.
Fetch the next digit (5) from the dividend, attach it to 2 and continue: 25 / 21

Moving on to step 2:
When dividing 25 by 21, we get 1 with a remainder of 4.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
If we take 21 away from 25, we end up with 4.
Append the next digit (3) from the dividend to 4 and continue with: 43 / 21

Going ahead to step 3:
The number 21 fits into 43 2 times, leaving a remainder of 1.
Write down 2 as next digit of the result. 
Result so far: 12.0
Subtracting 42 from 43 leaves us with 1.
Grab the next digit (0) from the dividend, add it to 1, then carry on: 10 / 21

Let's proceed to step 4:
If we divide 10 by 21, we get 0 and a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 120.0
Deduct 0 from 10 and we're left with 10.
Fetch the next digit (7) from the dividend, attach it to 10 and continue: 107 / 21

On to step 5:
When dividing 107 by 21, we get 5 with a remainder of 2.
The next digit of our result is 5. 
Result so far: 1205.0
Subtract 105 from 107 to get 2.
Take the next digit (5) from the dividend and append it to 2, then repeat: 25 / 21

Going ahead to step 6:
The number 21 fits into 25 1 times, leaving a remainder of 4.
Put 1 as the next digit of the answer. 
Result so far: 12051.0
Subtracting 21 from 25 leaves us with 4.
Take the next digit (6) from the dividend and append it to 4, then repeat: 46 / 21

Advancing to step 7:
If we divide 46 by 21, we get 2 and a remainder of 4.
The next digit of our result is 2. 
Result so far: 120512.0
Subtracting 42 from 46 leaves us with 4.
Take the next digit (8) from the dividend and append it to 4, then repeat: 48 / 21

Let's proceed to step 8:
If we divide 48 by 21, we get 2 and a remainder of 6.
Use 2 as the next digit of our solution. 
Result so far: 1205122.0
Subtract 42 from 48 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.

Let's proceed to step 9:
When dividing 60 by 21, we get 2 with a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 1205122.2
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.

On to step 10:
21 goes into 180 8 times with a remainder of 12.
The next digit of our result is 8. 
Result so far: 1205122.28
Subtracting 168 from 180 leaves us 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.

Going ahead to step 11:
120 divided by 21 is 5 with a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 1205122.285
Subtract 105 from 120 to get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Moving on to step 12:
150 divided by 21 is 7 with a remainder of 3.
Record the quotient 7 as the next digit in the result. 
Result so far: 1205122.2857
Subtracting 147 from 150 leaves us with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Moving on to step 13:
If we divide 30 by 21, we get 1 and a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 1205122.28571
If we subtract 21 from 30, we get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Going ahead to step 14:
The number 21 fits into 90 4 times, leaving a remainder of 6.
Write down 4 as next digit of the result. 
Result so far: 1205122.285714
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.

Moving on to step 15:
21 can be fit into 60 2 times, resulting in a remainder of 18.
Write down 2 as next digit of the result. 
Result so far: 1205122.2857142
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 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: 1205122.28571428
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.

The quotient of the division is 1205122.28571428, and the remainder is 1.2e-08.