571501 ÷ 21 
The aim is to understand the frequency of 21 in 571501.

Moving on to step 1:
21 goes into 5 0 times with a remainder of 5.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 5 and we're left with 5.
Take the next digit (7) from the dividend and append it to 5, then repeat: 57 / 21

Moving on to step 2:
When dividing 57 by 21, we get 2 with a remainder of 15.
Put 2 as the next digit of the answer. 
Result so far: 2.0
Deduct 42 from 57 and we're left with 15.
Include the next digit (1) from the dividend after 15, then repeat: 151 / 21

Going ahead to step 3:
21 can be fit into 151 7 times, resulting in a remainder of 4.
The number 7 becomes the next digit in our result. 
Result so far: 27.0
If we subtract 147 from 151, we get 4.
Append the next digit (5) from the dividend to 4 and continue with: 45 / 21

Moving on to step 4:
45 divided by 21 is 2 with a remainder of 3.
The number 2 becomes the next digit in our result. 
Result so far: 272.0
Subtracting 42 from 45 leaves us with 3.
Include the next digit (0) from the dividend after 3, then repeat: 30 / 21

Moving on to step 5:
21 goes into 30 1 times with a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 2721.0
Subtract 21 from 30 to get 9.
Take the next digit (1) from the dividend and append it to 9, then repeat: 91 / 21

On to step 6:
21 goes into 91 4 times with a remainder of 7.
Use 4 as the next digit of our solution. 
Result so far: 27214.0
Subtract 84 from 91 to get 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Step 7:
21 goes into 70 3 times with a remainder of 7.
Write down 3 as next digit of the result. 
Result so far: 27214.3
If we take 63 away from 70, we end up with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

Advancing to step 8:
The number 21 fits into 70 3 times, leaving a remainder of 7.
The number 3 becomes the next digit in our result. 
Result so far: 27214.33
Subtract 63 from 70 to get 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

The quotient of the division is 27214.33, and the remainder is 0.007.