828304 divided by 21 
The aim is to understand the frequency of 21 in 828304.

On to step 1:
8 divided by 21 is 0 with a remainder of 8.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtract 0 from 8 to get 8.
Include the next digit (2) from the dividend after 8, then repeat: 82 / 21

Let's proceed to step 2:
21 goes into 82 3 times with a remainder of 19.
Put 3 as the next digit of the answer. 
Result so far: 3.0
Deduct 63 from 82 and we're left with 19.
Fetch the next digit (8) from the dividend, attach it to 19 and continue: 198 / 21

Let's proceed to step 3:
21 goes into 198 9 times with a remainder of 9.
The next digit of our result is 9. 
Result so far: 39.0
Subtracting 189 from 198 leaves us with 9.
Bring next digit (3) of the dividend behind the 9 and repeat the process: 93 / 21

Let's proceed to step 4:
21 goes into 93 4 times with a remainder of 9.
Write down 4 as next digit of the result. 
Result so far: 394.0
If we subtract 84 from 93, we get 9.
Grab the next digit (0) from the dividend, add it to 9, then carry on: 90 / 21

Let's proceed to step 5:
When dividing 90 by 21, we get 4 with a remainder of 6.
Write down 4 as next digit of the result. 
Result so far: 3944.0
Subtract 84 from 90 to get 6.
Fetch the next digit (4) from the dividend, attach it to 6 and continue: 64 / 21

Going ahead to step 6:
64 divided by 21 is 3 with a remainder of 1.
Record the quotient 3 as the next digit in the result. 
Result so far: 39443.0
Subtracting 63 from 64 leaves us 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.

Advancing to step 7:
21 goes into 10 0 times with a remainder of 10.
The next digit of our result is 0. 
Result so far: 39443.0
If we subtract 0 from 10, we 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.

Advancing to step 8:
100 divided by 21 is 4 with a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 39443.04
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 9:
The number 21 fits into 160 7 times, leaving a remainder of 13.
The next digit of our result is 7. 
Result so far: 39443.047
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.

Advancing to step 10:
If we divide 130 by 21, we get 6 and a remainder of 4.
The number 6 becomes the next digit in our result. 
Result so far: 39443.0476
Deduct 126 from 130 and we're left with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Moving on to step 11:
The number 21 fits into 40 1 times, leaving a remainder of 19.
The number 1 becomes the next digit in our result. 
Result so far: 39443.04761
Deduct 21 from 40 and we're left with 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 12:
When dividing 190 by 21, we get 9 with a remainder of 1.
Use 9 as the next digit of our solution. 
Result so far: 39443.047619
The remainder is 1 after subtracting 189 from 190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Going ahead to step 13:
21 goes into 10 0 times with a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 39443.047619
The remainder is 10 after subtracting 0 from 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 14:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 39443.04761904
If we subtract 84 from 100, we 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.

The final outcome is 39443.04761904, with a leftover of 1.6e-08.