We look at the division of 748764 by 21 
The aim is to understand the frequency of 21 in 748764.

On to step 1:
7 divided by 21 is 0 with a remainder of 7.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtract 0 from 7 to get 7.
Fetch the next digit (4) from the dividend, attach it to 7 and continue: 74 / 21

Step 2:
21 goes into 74 3 times with a remainder of 11.
The number 3 becomes the next digit in our result. 
Result so far: 3.0
If we subtract 63 from 74, we get 11.
Take the next digit (8) from the dividend and append it to 11, then repeat: 118 / 21

Going ahead to step 3:
118 divided by 21 is 5 with a remainder of 13.
Put 5 as the next digit of the answer. 
Result so far: 35.0
Deduct 105 from 118 and we're left with 13.
Append the next digit (7) from the dividend to 13 and continue with: 137 / 21

Step 4:
137 divided by 21 is 6 with a remainder of 11.
Use 6 as the next digit of our solution. 
Result so far: 356.0
The remainder is 11 after subtracting 126 from 137.
Fetch the next digit (6) from the dividend, attach it to 11 and continue: 116 / 21

Advancing to step 5:
When dividing 116 by 21, we get 5 with a remainder of 11.
Write down 5 as next digit of the result. 
Result so far: 3565.0
If we subtract 105 from 116, we get 11.
Fetch the next digit (4) from the dividend, attach it to 11 and continue: 114 / 21

Moving on to step 6:
If we divide 114 by 21, we get 5 and a remainder of 9.
Put 5 as the next digit of the answer. 
Result so far: 35655.0
The remainder is 9 after subtracting 105 from 114.
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 7:
21 goes into 90 4 times with a remainder of 6.
The next digit of our result is 4. 
Result so far: 35655.4
Subtracting 84 from 90 leaves us with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Advancing to step 8:
The number 21 fits into 60 2 times, leaving a remainder of 18.
The next digit of our result is 2. 
Result so far: 35655.42
Deduct 42 from 60 and we're left 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.

Step 9:
If we divide 180 by 21, we get 8 and a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 35655.428
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.

On to step 10:
21 can be fit into 120 5 times, resulting in a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 35655.4285
If we subtract 105 from 120, we 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 11:
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: 35655.42857
Subtract 147 from 150 to get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Advancing to step 12:
The number 21 fits into 30 1 times, leaving a remainder of 9.
The next digit of our result is 1. 
Result so far: 35655.428571
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.

Step 13:
If we divide 90 by 21, we get 4 and a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 35655.4285714
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 14:
21 can be fit into 60 2 times, resulting in a remainder of 18.
The next digit of our result is 2. 
Result so far: 35655.42857142
If we subtract 42 from 60, we 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.

The final outcome is 35655.42857142, with a leftover of 1.8e-08.