We look at the division of 765486 by 21 
The aim is to understand the frequency of 21 in 765486.

On to step 1:
21 goes into 7 0 times with a remainder of 7.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 7, we get 7.
Take the next digit (6) from the dividend and append it to 7, then repeat: 76 / 21

Going ahead to step 2:
If we divide 76 by 21, we get 3 and a remainder of 13.
Record the quotient 3 as the next digit in the result. 
Result so far: 3.0
Subtract 63 from 76 to get 13.
Include the next digit (5) from the dividend after 13, then repeat: 135 / 21

Advancing to step 3:
The number 21 fits into 135 6 times, leaving a remainder of 9.
Use 6 as the next digit of our solution. 
Result so far: 36.0
Subtract 126 from 135 to get 9.
Append the next digit (4) from the dividend to 9 and continue with: 94 / 21

Step 4:
94 divided by 21 is 4 with a remainder of 10.
Put 4 as the next digit of the answer. 
Result so far: 364.0
If we take 84 away from 94, we end up with 10.
Fetch the next digit (8) from the dividend, attach it to 10 and continue: 108 / 21

Advancing to step 5:
When dividing 108 by 21, we get 5 with a remainder of 3.
Write down 5 as next digit of the result. 
Result so far: 3645.0
The remainder is 3 after subtracting 105 from 108.
Fetch the next digit (6) from the dividend, attach it to 3 and continue: 36 / 21

Advancing to step 6:
The number 21 fits into 36 1 times, leaving a remainder of 15.
Write down 1 as next digit of the result. 
Result so far: 36451.0
Subtract 21 from 36 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.

Let's proceed to step 7:
150 divided by 21 is 7 with a remainder of 3.
The next digit of our result is 7. 
Result so far: 36451.7
Deduct 147 from 150 and we're left 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.

Step 8:
21 goes into 30 1 times with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 36451.71
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.

Moving on to step 9:
The number 21 fits into 90 4 times, leaving a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 36451.714
If we subtract 84 from 90, we 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.

Going ahead to step 10:
21 can be fit into 60 2 times, resulting in a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 36451.7142
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.

On to step 11:
When dividing 180 by 21, we get 8 with a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 36451.71428
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.

Moving on to step 12:
21 goes into 120 5 times with a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 36451.714285
Deduct 105 from 120 and we're left with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Step 13:
21 goes into 150 7 times with a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 36451.7142857
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 14:
21 goes into 30 1 times with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 36451.71428571
If we take 21 away from 30, we end up 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.

The final result is 36451.71428571 with a remainder of 9e-09.