We look at the division of 51186761 by 21 
We're looking to find how many times 21 goes into 51186761.

Let's proceed to step 1:
21 can be fit into 5 0 times, resulting in a remainder of 5.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtracting 0 from 5 leaves us with 5.
Grab the next digit (1) from the dividend, add it to 5, then carry on: 51 / 21

Step 2:
21 goes into 51 2 times with a remainder of 9.
Write down 2 as next digit of the result. 
Result so far: 2.0
If we subtract 42 from 51, we get 9.
Append the next digit (1) from the dividend to 9 and continue with: 91 / 21

On to step 3:
If we divide 91 by 21, we get 4 and a remainder of 7.
Use 4 as the next digit of our solution. 
Result so far: 24.0
Deduct 84 from 91 and we're left with 7.
Fetch the next digit (8) from the dividend, attach it to 7 and continue: 78 / 21

On to step 4:
If we divide 78 by 21, we get 3 and a remainder of 15.
Record the quotient 3 as the next digit in the result. 
Result so far: 243.0
If we subtract 63 from 78, we get 15.
Fetch the next digit (6) from the dividend, attach it to 15 and continue: 156 / 21

On to step 5:
156 divided by 21 is 7 with a remainder of 9.
The next digit of our result is 7. 
Result so far: 2437.0
Deduct 147 from 156 and we're left with 9.
Fetch the next digit (7) from the dividend, attach it to 9 and continue: 97 / 21

Going ahead to step 6:
21 can be fit into 97 4 times, resulting in a remainder of 13.
The number 4 becomes the next digit in our result. 
Result so far: 24374.0
The remainder is 13 after subtracting 84 from 97.
Include the next digit (6) from the dividend after 13, then repeat: 136 / 21

Step 7:
When dividing 136 by 21, we get 6 with a remainder of 10.
Write down 6 as next digit of the result. 
Result so far: 243746.0
The remainder is 10 after subtracting 126 from 136.
Include the next digit (1) from the dividend after 10, then repeat: 101 / 21

On to step 8:
If we divide 101 by 21, we get 4 and a remainder of 17.
The next digit of our result is 4. 
Result so far: 2437464.0
The remainder is 17 after subtracting 84 from 101.
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 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: 2437464.8
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.

Let's proceed to step 10:
21 goes into 20 0 times with a remainder of 20.
Record the quotient 0 as the next digit in the result. 
Result so far: 2437464.8
If we subtract 0 from 20, we get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Advancing to step 11:
The number 21 fits into 200 9 times, leaving a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 2437464.809
Subtracting 189 from 200 leaves us 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 12:
110 divided by 21 is 5 with a remainder of 5.
The number 5 becomes the next digit in our result. 
Result so far: 2437464.8095
If we take 105 away from 110, we end up 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 13:
21 can be fit into 50 2 times, resulting in a remainder of 8.
Write down 2 as next digit of the result. 
Result so far: 2437464.80952
Deduct 42 from 50 and we're left 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.

Step 14:
When dividing 80 by 21, we get 3 with a remainder of 17.
Put 3 as the next digit of the answer. 
Result so far: 2437464.809523
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.

On to step 15:
21 goes into 170 8 times with a remainder of 2.
The number 8 becomes the next digit in our result. 
Result so far: 2437464.8095238
Subtracting 168 from 170 leaves us 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.

Advancing to step 16:
The number 21 fits into 20 0 times, leaving a remainder of 20.
The number 0 becomes the next digit in our result. 
Result so far: 2437464.8095238
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.

In conclusion, the division gives 2437464.8095238 with a balance of 2e-08.