We're dividing 408136 by 21 
We're looking to find how many times 21 goes into 408136.

On to step 1:
When dividing 4 by 21, we get 0 with a remainder of 4.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 4 to get 4.
Append the next digit (0) from the dividend to 4 and continue with: 40 / 21

Moving on to step 2:
40 divided by 21 is 1 with a remainder of 19.
Use 1 as the next digit of our solution. 
Result so far: 1.0
Deduct 21 from 40 and we're left with 19.
Take the next digit (8) from the dividend and append it to 19, then repeat: 198 / 21

Going ahead to step 3:
When dividing 198 by 21, we get 9 with a remainder of 9.
Record the quotient 9 as the next digit in the result. 
Result so far: 19.0
Deduct 189 from 198 and we're left with 9.
Append the next digit (1) from the dividend to 9 and continue with: 91 / 21

Going ahead to step 4:
If we divide 91 by 21, we get 4 and a remainder of 7.
Use 4 as the next digit of our solution. 
Result so far: 194.0
Subtract 84 from 91 to get 7.
Grab the next digit (3) from the dividend, add it to 7, then carry on: 73 / 21

Advancing to step 5:
If we divide 73 by 21, we get 3 and a remainder of 10.
The next digit of our result is 3. 
Result so far: 1943.0
If we subtract 63 from 73, we get 10.
Include the next digit (6) from the dividend after 10, then repeat: 106 / 21

On to step 6:
106 divided by 21 is 5 with a remainder of 1.
Use 5 as the next digit of our solution. 
Result so far: 19435.0
Deduct 105 from 106 and we're left with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

On to step 7:
If we divide 10 by 21, we get 0 and a remainder of 10.
The next digit of our result is 0. 
Result so far: 19435.0
Subtract 0 from 10 to get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

On to step 8:
21 goes into 100 4 times with a remainder of 16.
The next digit of our result is 4. 
Result so far: 19435.04
If we subtract 84 from 100, we get 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Step 9:
If we divide 160 by 21, we get 7 and a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 19435.047
The remainder is 13 after subtracting 147 from 160.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Advancing to step 10:
The number 21 fits into 130 6 times, leaving a remainder of 4.
Write down 6 as next digit of the result. 
Result so far: 19435.0476
Subtracting 126 from 130 leaves us with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Advancing to step 11:
The number 21 fits into 40 1 times, leaving a remainder of 19.
The number 1 becomes the next digit in our result. 
Result so far: 19435.04761
If we subtract 21 from 40, we get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Going ahead to step 12:
21 can be fit into 190 9 times, resulting in a remainder of 1.
The next digit of our result is 9. 
Result so far: 19435.047619
If we take 189 away from 190, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Let's proceed to step 13:
The number 21 fits into 10 0 times, leaving a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 19435.047619
Deduct 0 from 10 and we're left with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 14:
100 divided by 21 is 4 with a remainder of 16.
Put 4 as the next digit of the answer. 
Result so far: 19435.04761904
Subtracting 84 from 100 leaves us with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

The final outcome is 19435.04761904, with a leftover of 1.6e-08.