We're dividing 21231458 by 21 
We want to figure out the number of times 21231458 can be divided by 21.

On to step 1:
2 divided by 21 is 0 with a remainder of 2.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we subtract 0 from 2, we get 2.
Fetch the next digit (1) from the dividend, attach it to 2 and continue: 21 / 21

Step 2:
When dividing 21 by 21, we get 1 with a remainder of 0.
Use 1 as the next digit of our solution. 
Result so far: 1.0
Subtracting 21 from 21 leaves us with 0.
Bring next digit (2) of the dividend behind the 0 and repeat the process: 2 / 21

Let's proceed to step 3:
21 goes into 2 0 times with a remainder of 2.
The number 0 becomes the next digit in our result. 
Result so far: 10.0
Deduct 0 from 2 and we're left with 2.
Grab the next digit (3) from the dividend, add it to 2, then carry on: 23 / 21

Going ahead to step 4:
When dividing 23 by 21, we get 1 with a remainder of 2.
Use 1 as the next digit of our solution. 
Result so far: 101.0
The remainder is 2 after subtracting 21 from 23.
Include the next digit (1) from the dividend after 2, then repeat: 21 / 21

On to step 5:
When dividing 21 by 21, we get 1 with a remainder of 0.
Use 1 as the next digit of our solution. 
Result so far: 1011.0
If we take 21 away from 21, we end up with 0.
Grab the next digit (4) from the dividend, add it to 0, then carry on: 4 / 21

On to step 6:
21 can be fit into 4 0 times, resulting in a remainder of 4.
The number 0 becomes the next digit in our result. 
Result so far: 10110.0
Deduct 0 from 4 and we're left with 4.
Take the next digit (5) from the dividend and append it to 4, then repeat: 45 / 21

Step 7:
21 can be fit into 45 2 times, resulting in a remainder of 3.
The number 2 becomes the next digit in our result. 
Result so far: 101102.0
The remainder is 3 after subtracting 42 from 45.
Append the next digit (8) from the dividend to 3 and continue with: 38 / 21

Going ahead to step 8:
When dividing 38 by 21, we get 1 with a remainder of 17.
The number 1 becomes the next digit in our result. 
Result so far: 1011021.0
If we take 21 away from 38, we end up with 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Step 9:
170 divided by 21 is 8 with a remainder of 2.
The number 8 becomes the next digit in our result. 
Result so far: 1011021.8
The remainder is 2 after subtracting 168 from 170.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Going ahead to step 10:
20 divided by 21 is 0 with a remainder of 20.
Put 0 as the next digit of the answer. 
Result so far: 1011021.8
If we take 0 away from 20, we end up with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Step 11:
21 goes into 200 9 times with a remainder of 11.
The number 9 becomes the next digit in our result. 
Result so far: 1011021.809
The remainder is 11 after subtracting 189 from 200.
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 12:
When dividing 110 by 21, we get 5 with a remainder of 5.
The next digit of our result is 5. 
Result so far: 1011021.8095
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.

Moving on to step 13:
If we divide 50 by 21, we get 2 and a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 1011021.80952
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.

Let's proceed to step 14:
If we divide 80 by 21, we get 3 and a remainder of 17.
Record the quotient 3 as the next digit in the result. 
Result so far: 1011021.809523
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.

Moving on to step 15:
The number 21 fits into 170 8 times, leaving a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 1011021.8095238
If we subtract 168 from 170, we 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.

Step 16:
21 can be fit into 20 0 times, resulting in a remainder of 20.
Write down 0 as next digit of the result. 
Result so far: 1011021.8095238
Subtracting 0 from 20 leaves us with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

The final result is 1011021.8095238 with a remainder of 2e-08.