17015 divided by 21 
The aim is to understand the frequency of 21 in 17015.

Going ahead to step 1:
If we divide 1 by 21, we get 0 and a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 1, we end up with 1.
Take the next digit (7) from the dividend and append it to 1, then repeat: 17 / 21

Advancing to step 2:
The number 21 fits into 17 0 times, leaving a remainder of 17.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtracting 0 from 17 leaves us with 17.
Grab the next digit (0) from the dividend, add it to 17, then carry on: 170 / 21

Step 3:
21 goes into 170 8 times with a remainder of 2.
Write down 8 as next digit of the result. 
Result so far: 8.0
If we take 168 away from 170, we end up with 2.
Grab the next digit (1) from the dividend, add it to 2, then carry on: 21 / 21

Going ahead to step 4:
When dividing 21 by 21, we get 1 with a remainder of 0.
The number 1 becomes the next digit in our result. 
Result so far: 81.0
Subtracting 21 from 21 leaves us with 0.
Include the next digit (5) from the dividend after 0, then repeat: 5 / 21

Let's proceed to step 5:
When dividing 5 by 21, we get 0 with a remainder of 5.
The next digit of our result is 0. 
Result so far: 810.0
Subtracting 0 from 5 leaves us with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Step 6:
If we divide 50 by 21, we get 2 and a remainder of 8.
Record the quotient 2 as the next digit in the result. 
Result so far: 810.2
Deduct 42 from 50 and we're left with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Advancing to step 7:
21 can be fit into 80 3 times, resulting in a remainder of 17.
Use 3 as the next digit of our solution. 
Result so far: 810.23
If we take 63 away from 80, we end up with 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Let's proceed to step 8:
21 can be fit into 170 8 times, resulting in a remainder of 2.
Record the quotient 8 as the next digit in the result. 
Result so far: 810.238
The remainder is 2 after subtracting 168 from 170.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Going ahead to step 9:
The number 21 fits into 20 0 times, leaving a remainder of 20.
Record the quotient 0 as the next digit in the result. 
Result so far: 810.238
The remainder is 20 after subtracting 0 from 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Going ahead to step 10:
When dividing 200 by 21, we get 9 with a remainder of 11.
Use 9 as the next digit of our solution. 
Result so far: 810.23809
Subtract 189 from 200 to get 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Advancing to step 11:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 810.238095
If we subtract 105 from 110, we get 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Step 12:
If we divide 50 by 21, we get 2 and a remainder of 8.
Record the quotient 2 as the next digit in the result. 
Result so far: 810.2380952
Subtracting 42 from 50 leaves us with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Step 13:
When dividing 80 by 21, we get 3 with a remainder of 17.
Put 3 as the next digit of the answer. 
Result so far: 810.23809523
Subtract 63 from 80 to get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

The final result is 810.23809523 with a remainder of 1.7e-08.