405175 divided by 21 
We're looking to find how many times 21 goes into 405175.

Step 1:
When dividing 4 by 21, we get 0 with a remainder of 4.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtracting 0 from 4 leaves us with 4.
Bring next digit (0) of the dividend behind the 4 and repeat the process: 40 / 21

Advancing to step 2:
The number 21 fits into 40 1 times, leaving a remainder of 19.
Put 1 as the next digit of the answer. 
Result so far: 1.0
The remainder is 19 after subtracting 21 from 40.
Bring next digit (5) of the dividend behind the 19 and repeat the process: 195 / 21

On to step 3:
When dividing 195 by 21, we get 9 with a remainder of 6.
Record the quotient 9 as the next digit in the result. 
Result so far: 19.0
Deduct 189 from 195 and we're left with 6.
Bring next digit (1) of the dividend behind the 6 and repeat the process: 61 / 21

On to step 4:
The number 21 fits into 61 2 times, leaving a remainder of 19.
The next digit of our result is 2. 
Result so far: 192.0
Deduct 42 from 61 and we're left with 19.
Fetch the next digit (7) from the dividend, attach it to 19 and continue: 197 / 21

Advancing to step 5:
The number 21 fits into 197 9 times, leaving a remainder of 8.
Use 9 as the next digit of our solution. 
Result so far: 1929.0
Subtracting 189 from 197 leaves us with 8.
Fetch the next digit (5) from the dividend, attach it to 8 and continue: 85 / 21

On to step 6:
If we divide 85 by 21, we get 4 and a remainder of 1.
The number 4 becomes the next digit in our result. 
Result so far: 19294.0
The remainder is 1 after subtracting 84 from 85.
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:
When dividing 10 by 21, we get 0 with a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 19294.0
If we take 0 away from 10, we end up 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.

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: 19294.04
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.

Going ahead to step 9:
When dividing 160 by 21, we get 7 with a remainder of 13.
The next digit of our result is 7. 
Result so far: 19294.047
Deduct 147 from 160 and we're left with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Going ahead to step 10:
21 goes into 130 6 times with a remainder of 4.
Record the quotient 6 as the next digit in the result. 
Result so far: 19294.0476
If we subtract 126 from 130, we get 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:
21 can be fit into 40 1 times, resulting in a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 19294.04761
The remainder is 19 after subtracting 21 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Let's proceed to step 12:
The number 21 fits into 190 9 times, leaving a remainder of 1.
Put 9 as the next digit of the answer. 
Result so far: 19294.047619
If we subtract 189 from 190, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Moving on to step 13:
21 goes into 10 0 times with a remainder of 10.
Write down 0 as next digit of the result. 
Result so far: 19294.047619
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.

Step 14:
The number 21 fits into 100 4 times, leaving a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 19294.04761904
If we take 84 away from 100, we end up 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 19294.04761904, with a leftover of 1.6e-08.