We look at the division of 262160 by 21 
The aim is to understand the frequency of 21 in 262160.

On to step 1:
2 divided by 21 is 0 with a remainder of 2.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtracting 0 from 2 leaves us with 2.
Grab the next digit (6) from the dividend, add it to 2, then carry on: 26 / 21

Step 2:
The number 21 fits into 26 1 times, leaving a remainder of 5.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
Deduct 21 from 26 and we're left with 5.
Take the next digit (2) from the dividend and append it to 5, then repeat: 52 / 21

On to step 3:
21 goes into 52 2 times with a remainder of 10.
Put 2 as the next digit of the answer. 
Result so far: 12.0
Subtracting 42 from 52 leaves us with 10.
Bring next digit (1) of the dividend behind the 10 and repeat the process: 101 / 21

On to step 4:
21 goes into 101 4 times with a remainder of 17.
The next digit of our result is 4. 
Result so far: 124.0
If we take 84 away from 101, we end up with 17.
Fetch the next digit (6) from the dividend, attach it to 17 and continue: 176 / 21

Step 5:
21 goes into 176 8 times with a remainder of 8.
The next digit of our result is 8. 
Result so far: 1248.0
If we subtract 168 from 176, we get 8.
Include the next digit (0) from the dividend after 8, then repeat: 80 / 21

On to step 6:
21 can be fit into 80 3 times, resulting in a remainder of 17.
Record the quotient 3 as the next digit in the result. 
Result so far: 12483.0
If we subtract 63 from 80, we get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Step 7:
When dividing 170 by 21, we get 8 with a remainder of 2.
Record the quotient 8 as the next digit in the result. 
Result so far: 12483.8
Deduct 168 from 170 and we're left 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.

Step 8:
The number 21 fits into 20 0 times, leaving a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 12483.8
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.

Advancing to step 9:
The number 21 fits into 200 9 times, leaving a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 12483.809
Subtracting 189 from 200 leaves us with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Step 10:
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: 12483.8095
Subtract 105 from 110 to get 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Moving on to step 11:
21 goes into 50 2 times with a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 12483.80952
Deduct 42 from 50 and we're left with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Moving on to step 12:
If we divide 80 by 21, we get 3 and a remainder of 17.
The number 3 becomes the next digit in our result. 
Result so far: 12483.809523
Subtract 63 from 80 to get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Step 13:
The number 21 fits into 170 8 times, leaving a remainder of 2.
Put 8 as the next digit of the answer. 
Result so far: 12483.8095238
Subtract 168 from 170 to get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Advancing to step 14:
21 can be fit into 20 0 times, resulting in a remainder of 20.
The number 0 becomes the next digit in our result. 
Result so far: 12483.8095238
Subtract 0 from 20 to get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

The final result is 12483.8095238 with a remainder of 2e-08.