828724 divided by 21 
The aim is to understand the frequency of 21 in 828724.

Let's proceed to step 1:
8 divided by 21 is 0 with a remainder of 8.
Put 0 as the next digit of the answer. 
Result so far: 0.0
The remainder is 8 after subtracting 0 from 8.
Append the next digit (2) from the dividend to 8 and continue with: 82 / 21

Let's proceed to step 2:
The number 21 fits into 82 3 times, leaving a remainder of 19.
The next digit of our result is 3. 
Result so far: 3.0
Subtracting 63 from 82 leaves us with 19.
Include the next digit (8) from the dividend after 19, then repeat: 198 / 21

On to step 3:
If we divide 198 by 21, we get 9 and a remainder of 9.
Write down 9 as next digit of the result. 
Result so far: 39.0
Subtract 189 from 198 to get 9.
Fetch the next digit (7) from the dividend, attach it to 9 and continue: 97 / 21

Let's proceed to step 4:
97 divided by 21 is 4 with a remainder of 13.
Write down 4 as next digit of the result. 
Result so far: 394.0
Subtract 84 from 97 to get 13.
Grab the next digit (2) from the dividend, add it to 13, then carry on: 132 / 21

On to step 5:
When dividing 132 by 21, we get 6 with a remainder of 6.
Record the quotient 6 as the next digit in the result. 
Result so far: 3946.0
If we take 126 away from 132, we end up with 6.
Fetch the next digit (4) from the dividend, attach it to 6 and continue: 64 / 21

Let's proceed to step 6:
21 goes into 64 3 times with a remainder of 1.
The number 3 becomes the next digit in our result. 
Result so far: 39463.0
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.

Let's proceed to step 7:
21 goes into 10 0 times with a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 39463.0
If we take 0 away from 10, we end up 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.

Going ahead to step 8:
The number 21 fits into 100 4 times, leaving a remainder of 16.
The next digit of our result is 4. 
Result so far: 39463.04
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.

Advancing to step 9:
If we divide 160 by 21, we get 7 and a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 39463.047
If we subtract 147 from 160, we get 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:
The number 21 fits into 130 6 times, leaving a remainder of 4.
The next digit of our result is 6. 
Result so far: 39463.0476
Subtracting 126 from 130 leaves us 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.

On to step 11:
21 can be fit into 40 1 times, resulting in a remainder of 19.
The next digit of our result is 1. 
Result so far: 39463.04761
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.

On to step 12:
The number 21 fits into 190 9 times, leaving a remainder of 1.
Put 9 as the next digit of the answer. 
Result so far: 39463.047619
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.

On to step 13:
When dividing 10 by 21, we get 0 with a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 39463.047619
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.

Going ahead to step 14:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Put 4 as the next digit of the answer. 
Result so far: 39463.04761904
If we take 84 away from 100, we end up with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Our division results in 39463.04761904 with a remaining 1.6e-08.