We're dividing 215861 by 21 
We want to figure out the number of times 215861 can be divided by 21.

On to step 1:
21 can be fit into 2 0 times, resulting in a remainder of 2.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 2 to get 2.
Append the next digit (1) from the dividend to 2 and continue with: 21 / 21

On to step 2:
21 goes into 21 1 times with a remainder of 0.
Use 1 as the next digit of our solution. 
Result so far: 1.0
Subtract 21 from 21 to get 0.
Take the next digit (5) from the dividend and append it to 0, then repeat: 5 / 21

Going ahead to step 3:
21 can be fit into 5 0 times, resulting in a remainder of 5.
The next digit of our result is 0. 
Result so far: 10.0
Deduct 0 from 5 and we're left with 5.
Append the next digit (8) from the dividend to 5 and continue with: 58 / 21

On to step 4:
If we divide 58 by 21, we get 2 and a remainder of 16.
Put 2 as the next digit of the answer. 
Result so far: 102.0
Subtracting 42 from 58 leaves us with 16.
Include the next digit (6) from the dividend after 16, then repeat: 166 / 21

Step 5:
The number 21 fits into 166 7 times, leaving a remainder of 19.
The number 7 becomes the next digit in our result. 
Result so far: 1027.0
Subtracting 147 from 166 leaves us with 19.
Grab the next digit (1) from the dividend, add it to 19, then carry on: 191 / 21

Advancing to step 6:
When dividing 191 by 21, we get 9 with a remainder of 2.
The next digit of our result is 9. 
Result so far: 10279.0
Subtract 189 from 191 to get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Advancing to step 7:
If we divide 20 by 21, we get 0 and a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 10279.0
Subtract 0 from 20 to get 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 8:
If we divide 200 by 21, we get 9 and a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 10279.09
Subtracting 189 from 200 leaves us with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Moving on to step 9:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Record the quotient 5 as the next digit in the result. 
Result so far: 10279.095
Subtracting 105 from 110 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.

Advancing to step 10:
21 can be fit into 50 2 times, resulting in a remainder of 8.
The next digit of our result is 2. 
Result so far: 10279.0952
If we take 42 away from 50, we end up 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.

Moving on to step 11:
80 divided by 21 is 3 with a remainder of 17.
The next digit of our result is 3. 
Result so far: 10279.09523
The remainder is 17 after subtracting 63 from 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Advancing to step 12:
When dividing 170 by 21, we get 8 with a remainder of 2.
The number 8 becomes the next digit in our result. 
Result so far: 10279.095238
Subtract 168 from 170 to get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Moving on to step 13:
21 can be fit into 20 0 times, resulting in a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 10279.095238
If we subtract 0 from 20, we get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

On to step 14:
200 divided by 21 is 9 with a remainder of 11.
The number 9 becomes the next digit in our result. 
Result so far: 10279.09523809
Deduct 189 from 200 and we're left with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

The final outcome is 10279.09523809, with a leftover of 1.1e-08.