Let's divide 171210 by 21
We want to figure out the number of times 171210 can be divided by 21.

Advancing to step 1:
If we divide 1 by 21, we get 0 and a remainder of 1.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we subtract 0 from 1, we get 1.
Take the next digit (7) from the dividend and append it to 1, then repeat: 17 / 21

Let's proceed to step 2:
When dividing 17 by 21, we get 0 with a remainder of 17.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 17, we end up with 17.
Include the next digit (1) from the dividend after 17, then repeat: 171 / 21

Going ahead to step 3:
21 goes into 171 8 times with a remainder of 3.
The next digit of our result is 8. 
Result so far: 8.0
The remainder is 3 after subtracting 168 from 171.
Include the next digit (2) from the dividend after 3, then repeat: 32 / 21

On to step 4:
21 goes into 32 1 times with a remainder of 11.
Use 1 as the next digit of our solution. 
Result so far: 81.0
Subtracting 21 from 32 leaves us with 11.
Grab the next digit (1) from the dividend, add it to 11, then carry on: 111 / 21

Step 5:
111 divided by 21 is 5 with a remainder of 6.
Record the quotient 5 as the next digit in the result. 
Result so far: 815.0
Subtracting 105 from 111 leaves us with 6.
Take the next digit (0) from the dividend and append it to 6, then repeat: 60 / 21

Moving on to step 6:
21 goes into 60 2 times with a remainder of 18.
The next digit of our result is 2. 
Result so far: 8152.0
Deduct 42 from 60 and we're left with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

On to step 7:
21 can be fit into 180 8 times, resulting in a remainder of 12.
Put 8 as the next digit of the answer. 
Result so far: 8152.8
The remainder is 12 after subtracting 168 from 180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Going ahead to step 8:
When dividing 120 by 21, we get 5 with a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 8152.85
Subtract 105 from 120 to get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Going ahead to step 9:
If we divide 150 by 21, we get 7 and a remainder of 3.
The next digit of our result is 7. 
Result so far: 8152.857
If we subtract 147 from 150, we get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 10:
When dividing 30 by 21, we get 1 with a remainder of 9.
Record the quotient 1 as the next digit in the result. 
Result so far: 8152.8571
Subtract 21 from 30 to get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Going ahead to step 11:
If we divide 90 by 21, we get 4 and a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 8152.85714
Subtract 84 from 90 to get 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Step 12:
The number 21 fits into 60 2 times, leaving a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 8152.857142
Subtract 42 from 60 to get 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

On to step 13:
21 goes into 180 8 times with a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 8152.8571428
Subtracting 168 from 180 leaves us with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

On to step 14:
When dividing 120 by 21, we get 5 with a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 8152.85714285
Subtracting 105 from 120 leaves us with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

The final outcome is 8152.85714285, with a leftover of 1.5e-08.