We're dividing 868253 by 21 
The aim is to understand the frequency of 21 in 868253.

Let's proceed to step 1:
When dividing 8 by 21, we get 0 with a remainder of 8.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we take 0 away from 8, we end up with 8.
Include the next digit (6) from the dividend after 8, then repeat: 86 / 21

Let's proceed to step 2:
If we divide 86 by 21, we get 4 and a remainder of 2.
The next digit of our result is 4. 
Result so far: 4.0
The remainder is 2 after subtracting 84 from 86.
Grab the next digit (8) from the dividend, add it to 2, then carry on: 28 / 21

Moving on to step 3:
When dividing 28 by 21, we get 1 with a remainder of 7.
Use 1 as the next digit of our solution. 
Result so far: 41.0
Subtracting 21 from 28 leaves us with 7.
Bring next digit (2) of the dividend behind the 7 and repeat the process: 72 / 21

Let's proceed to step 4:
21 goes into 72 3 times with a remainder of 9.
Record the quotient 3 as the next digit in the result. 
Result so far: 413.0
Subtracting 63 from 72 leaves us with 9.
Include the next digit (5) from the dividend after 9, then repeat: 95 / 21

Moving on to step 5:
The number 21 fits into 95 4 times, leaving a remainder of 11.
Write down 4 as next digit of the result. 
Result so far: 4134.0
Deduct 84 from 95 and we're left with 11.
Fetch the next digit (3) from the dividend, attach it to 11 and continue: 113 / 21

Step 6:
21 goes into 113 5 times with a remainder of 8.
Record the quotient 5 as the next digit in the result. 
Result so far: 41345.0
Subtract 105 from 113 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.

Moving on to step 7:
21 goes into 80 3 times with a remainder of 17.
Write down 3 as next digit of the result. 
Result so far: 41345.3
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.

On to step 8:
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: 41345.38
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.

Going ahead to step 9:
21 goes into 20 0 times with a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 41345.38
Deduct 0 from 20 and we're left 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 10:
200 divided by 21 is 9 with a remainder of 11.
Use 9 as the next digit of our solution. 
Result so far: 41345.3809
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 11:
The number 21 fits into 110 5 times, leaving a remainder of 5.
Use 5 as the next digit of our solution. 
Result so far: 41345.38095
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.

Let's proceed to step 12:
21 can be fit into 50 2 times, resulting in a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 41345.380952
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.

Going ahead to step 13:
When dividing 80 by 21, we get 3 with a remainder of 17.
The next digit of our result is 3. 
Result so far: 41345.3809523
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.

Advancing to step 14:
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: 41345.38095238
If we subtract 168 from 170, we 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.

The final outcome is 41345.38095238, with a leftover of 2e-09.