We look at the division of 306304 by 21 
The aim is to understand the frequency of 21 in 306304.

Going ahead to step 1:
3 divided by 21 is 0 with a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
The remainder is 3 after subtracting 0 from 3.
Take the next digit (0) from the dividend and append it to 3, then repeat: 30 / 21

Advancing to step 2:
21 goes into 30 1 times with a remainder of 9.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
Subtract 21 from 30 to get 9.
Grab the next digit (6) from the dividend, add it to 9, then carry on: 96 / 21

On to step 3:
The number 21 fits into 96 4 times, leaving a remainder of 12.
The next digit of our result is 4. 
Result so far: 14.0
The remainder is 12 after subtracting 84 from 96.
Grab the next digit (3) from the dividend, add it to 12, then carry on: 123 / 21

Step 4:
123 divided by 21 is 5 with a remainder of 18.
Record the quotient 5 as the next digit in the result. 
Result so far: 145.0
Subtract 105 from 123 to get 18.
Take the next digit (0) from the dividend and append it to 18, then repeat: 180 / 21

Let's proceed to step 5:
21 goes into 180 8 times with a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 1458.0
Subtract 168 from 180 to get 12.
Append the next digit (4) from the dividend to 12 and continue with: 124 / 21

Moving on to step 6:
If we divide 124 by 21, we get 5 and a remainder of 19.
Write down 5 as next digit of the result. 
Result so far: 14585.0
If we subtract 105 from 124, we get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Moving on to step 7:
21 can be fit into 190 9 times, resulting in a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 14585.9
Deduct 189 from 190 and we're left with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Let's proceed to step 8:
If we divide 10 by 21, we get 0 and a remainder of 10.
The next digit of our result is 0. 
Result so far: 14585.9
Deduct 0 from 10 and we're left with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 9:
100 divided by 21 is 4 with a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 14585.904
Subtract 84 from 100 to get 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Going ahead to step 10:
When dividing 160 by 21, we get 7 with a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 14585.9047
Deduct 147 from 160 and we're left with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Moving on to step 11:
The number 21 fits into 130 6 times, leaving a remainder of 4.
The next digit of our result is 6. 
Result so far: 14585.90476
The remainder is 4 after subtracting 126 from 130.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Step 12:
The number 21 fits into 40 1 times, leaving a remainder of 19.
The next digit of our result is 1. 
Result so far: 14585.904761
Subtract 21 from 40 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Step 13:
The number 21 fits into 190 9 times, leaving a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 14585.9047619
Subtract 189 from 190 to get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Moving on to step 14:
The number 21 fits into 10 0 times, leaving a remainder of 10.
The number 0 becomes the next digit in our result. 
Result so far: 14585.9047619
Subtract 0 from 10 to get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

The quotient of the division is 14585.9047619, and the remainder is 1e-08.