421689 ÷ 21 
Our goal is to divide 421689 by 21.

Advancing to step 1:
21 goes into 4 0 times with a remainder of 4.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
The remainder is 4 after subtracting 0 from 4.
Bring next digit (2) of the dividend behind the 4 and repeat the process: 42 / 21

Let's proceed to step 2:
21 goes into 42 2 times with a remainder of 0.
Put 2 as the next digit of the answer. 
Result so far: 2.0
If we take 42 away from 42, we end up with 0.
Include the next digit (1) from the dividend after 0, then repeat: 1 / 21

Let's proceed to step 3:
The number 21 fits into 1 0 times, leaving a remainder of 1.
Write down 0 as next digit of the result. 
Result so far: 20.0
Subtract 0 from 1 to get 1.
Bring next digit (6) of the dividend behind the 1 and repeat the process: 16 / 21

Let's proceed to step 4:
If we divide 16 by 21, we get 0 and a remainder of 16.
The number 0 becomes the next digit in our result. 
Result so far: 200.0
Deduct 0 from 16 and we're left with 16.
Include the next digit (8) from the dividend after 16, then repeat: 168 / 21

Step 5:
21 goes into 168 8 times with a remainder of 0.
Record the quotient 8 as the next digit in the result. 
Result so far: 2008.0
If we take 168 away from 168, we end up with 0.
Include the next digit (9) from the dividend after 0, then repeat: 9 / 21

Advancing to step 6:
21 goes into 9 0 times with a remainder of 9.
Put 0 as the next digit of the answer. 
Result so far: 20080.0
If we take 0 away from 9, we end up 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.

Moving on to step 7:
If we divide 90 by 21, we get 4 and a remainder of 6.
Write down 4 as next digit of the result. 
Result so far: 20080.4
The remainder is 6 after subtracting 84 from 90.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Let's proceed to step 8:
21 can be fit into 60 2 times, resulting in a remainder of 18.
The next digit of our result is 2. 
Result so far: 20080.42
If we take 42 away from 60, we end up with 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 9:
180 divided by 21 is 8 with a remainder of 12.
The next digit of our result is 8. 
Result so far: 20080.428
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.

Let's proceed to step 10:
When dividing 120 by 21, we get 5 with a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 20080.4285
If we take 105 away from 120, we end up 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.

Going ahead to step 11:
The number 21 fits into 150 7 times, leaving a remainder of 3.
Record the quotient 7 as the next digit in the result. 
Result so far: 20080.42857
Subtracting 147 from 150 leaves us with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 12:
21 goes into 30 1 times with a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 20080.428571
If we subtract 21 from 30, we get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Let's proceed to step 13:
90 divided by 21 is 4 with a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 20080.4285714
Subtracting 84 from 90 leaves us with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Let's proceed to step 14:
21 can be fit into 60 2 times, resulting in a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 20080.42857142
If we take 42 away from 60, we end up with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

The quotient of the division is 20080.42857142, and the remainder is 1.8e-08.