391511 divided by 21 
We want to divide 391511 by 21.

Going ahead to step 1:
The number 21 fits into 3 0 times, leaving a remainder of 3.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 3 to get 3.
Bring next digit (9) of the dividend behind the 3 and repeat the process: 39 / 21

Step 2:
39 divided by 21 is 1 with a remainder of 18.
Write down 1 as next digit of the result. 
Result so far: 1.0
Subtract 21 from 39 to get 18.
Include the next digit (1) from the dividend after 18, then repeat: 181 / 21

Moving on to step 3:
21 goes into 181 8 times with a remainder of 13.
Record the quotient 8 as the next digit in the result. 
Result so far: 18.0
The remainder is 13 after subtracting 168 from 181.
Grab the next digit (5) from the dividend, add it to 13, then carry on: 135 / 21

Let's proceed to step 4:
When dividing 135 by 21, we get 6 with a remainder of 9.
Record the quotient 6 as the next digit in the result. 
Result so far: 186.0
The remainder is 9 after subtracting 126 from 135.
Fetch the next digit (1) from the dividend, attach it to 9 and continue: 91 / 21

Going ahead to step 5:
21 can be fit into 91 4 times, resulting in a remainder of 7.
Record the quotient 4 as the next digit in the result. 
Result so far: 1864.0
If we take 84 away from 91, we end up with 7.
Grab the next digit (1) from the dividend, add it to 7, then carry on: 71 / 21

Advancing to step 6:
71 divided by 21 is 3 with a remainder of 8.
Record the quotient 3 as the next digit in the result. 
Result so far: 18643.0
Subtracting 63 from 71 leaves us 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.

Moving on to step 7:
21 can be fit into 80 3 times, resulting in a remainder of 17.
The next digit of our result is 3. 
Result so far: 18643.3
If we subtract 63 from 80, we get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

On to step 8:
21 goes into 170 8 times with a remainder of 2.
The number 8 becomes the next digit in our result. 
Result so far: 18643.38
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.

Let's proceed to step 9:
21 can be fit into 20 0 times, resulting in a remainder of 20.
The next digit of our result is 0. 
Result so far: 18643.38
Deduct 0 from 20 and we're left 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.

Moving on to step 10:
21 can be fit into 200 9 times, resulting in a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 18643.3809
Deduct 189 from 200 and we're left with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Step 11:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Record the quotient 5 as the next digit in the result. 
Result so far: 18643.38095
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.

Going ahead to step 12:
When dividing 50 by 21, we get 2 with a remainder of 8.
Put 2 as the next digit of the answer. 
Result so far: 18643.380952
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.

Moving on to step 13:
21 goes into 80 3 times with a remainder of 17.
Record the quotient 3 as the next digit in the result. 
Result so far: 18643.3809523
Deduct 63 from 80 and we're left 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 14:
170 divided by 21 is 8 with a remainder of 2.
The number 8 becomes the next digit in our result. 
Result so far: 18643.38095238
If we take 168 away from 170, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

The final outcome is 18643.38095238, with a leftover of 2e-09.