866100 divided by 21 
We want to figure out the number of times 866100 can be divided by 21.

Going ahead to step 1:
21 goes into 8 0 times with a remainder of 8.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 8 and we're left with 8.
Include the next digit (6) from the dividend after 8, then repeat: 86 / 21

Step 2:
If we divide 86 by 21, we get 4 and a remainder of 2.
Use 4 as the next digit of our solution. 
Result so far: 4.0
Subtract 84 from 86 to get 2.
Fetch the next digit (6) from the dividend, attach it to 2 and continue: 26 / 21

Advancing to step 3:
If we divide 26 by 21, we get 1 and a remainder of 5.
The next digit of our result is 1. 
Result so far: 41.0
If we subtract 21 from 26, we get 5.
Fetch the next digit (1) from the dividend, attach it to 5 and continue: 51 / 21

Advancing to step 4:
21 can be fit into 51 2 times, resulting in a remainder of 9.
Record the quotient 2 as the next digit in the result. 
Result so far: 412.0
Deduct 42 from 51 and we're left with 9.
Take the next digit (0) from the dividend and append it to 9, then repeat: 90 / 21

Step 5:
21 can be fit into 90 4 times, resulting in a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 4124.0
If we subtract 84 from 90, we get 6.
Include the next digit (0) from the dividend after 6, then repeat: 60 / 21

Going ahead to step 6:
If we divide 60 by 21, we get 2 and a remainder of 18.
Write down 2 as next digit of the result. 
Result so far: 41242.0
The remainder is 18 after subtracting 42 from 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Let's proceed to step 7:
The number 21 fits into 180 8 times, leaving a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 41242.8
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.

Let's proceed to step 8:
21 can be fit into 120 5 times, resulting in a remainder of 15.
Use 5 as the next digit of our solution. 
Result so far: 41242.85
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.

Moving on 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: 41242.857
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.

On to step 10:
21 goes into 30 1 times with a remainder of 9.
Put 1 as the next digit of the answer. 
Result so far: 41242.8571
Deduct 21 from 30 and we're left with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

On to step 11:
21 goes into 90 4 times with a remainder of 6.
The next digit of our result is 4. 
Result so far: 41242.85714
If we subtract 84 from 90, we 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.

On to step 12:
60 divided by 21 is 2 with a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 41242.857142
If we subtract 42 from 60, we 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.

Going ahead to step 13:
If we divide 180 by 21, we get 8 and a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 41242.8571428
Deduct 168 from 180 and we're left 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.

Advancing to step 14:
21 goes into 120 5 times with a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 41242.85714285
The remainder is 15 after subtracting 105 from 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

After the division, we end up with 41242.85714285 and a remainder of 1.5e-08.