Let's divide 420609 by 21
Our goal is to divide 420609 by 21.

Advancing 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
If we subtract 0 from 4, we get 4.
Include the next digit (2) from the dividend after 4, then repeat: 42 / 21

Going ahead to step 2:
21 can be fit into 42 2 times, resulting in a remainder of 0.
The next digit of our result is 2. 
Result so far: 2.0
Deduct 42 from 42 and we're left with 0.
Fetch the next digit (0) from the dividend, attach it to 0 and continue: 0 / 21

Moving on to step 3:
0 divided by 21 is 0 with a remainder of 0.
Record the quotient 0 as the next digit in the result. 
Result so far: 20.0
If we subtract 0 from 0, we get 0.
Fetch the next digit (6) from the dividend, attach it to 0 and continue: 6 / 21

Advancing to step 4:
The number 21 fits into 6 0 times, leaving a remainder of 6.
The number 0 becomes the next digit in our result. 
Result so far: 200.0
Subtract 0 from 6 to get 6.
Append the next digit (0) from the dividend to 6 and continue with: 60 / 21

On to step 5:
60 divided by 21 is 2 with a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 2002.0
If we subtract 42 from 60, we get 18.
Grab the next digit (9) from the dividend, add it to 18, then carry on: 189 / 21

Step 6:
189 divided by 21 is 9 with a remainder of 0.
The next digit of our result is 9. 
Result so far: 20029.0
The remainder is 0 after subtracting 189 from 189.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

On to step 7:
When dividing 0 by 21, we get 0 with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 20029.0
Deduct 0 from 0 and we're left with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Let's proceed to step 8:
21 goes into 0 0 times with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 20029.0
The remainder is 0 after subtracting 0 from 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Our division results in 20029.0 with a remaining 0.0.