We look at the division of 21639887 by 420 
We want to figure out the number of times 21639887 can be divided by 420.

Advancing to step 1:
420 can be fit into 2 0 times, resulting in a remainder of 2.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 2, we get 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 420

Advancing to step 2:
When dividing 21 by 420, we get 0 with a remainder of 21.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 21, we end up with 21.
Take the next digit (6) from the dividend and append it to 21, then repeat: 216 / 420

Moving on to step 3:
The number 420 fits into 216 0 times, leaving a remainder of 216.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we take 0 away from 216, we end up with 216.
Take the next digit (3) from the dividend and append it to 216, then repeat: 2163 / 420

Moving on to step 4:
420 goes into 2163 5 times with a remainder of 63.
The number 5 becomes the next digit in our result. 
Result so far: 5.0
The remainder is 63 after subtracting 2100 from 2163.
Take the next digit (9) from the dividend and append it to 63, then repeat: 639 / 420

On to step 5:
If we divide 639 by 420, we get 1 and a remainder of 219.
Use 1 as the next digit of our solution. 
Result so far: 51.0
Subtracting 420 from 639 leaves us with 219.
Append the next digit (8) from the dividend to 219 and continue with: 2198 / 420

Going ahead to step 6:
If we divide 2198 by 420, we get 5 and a remainder of 98.
Put 5 as the next digit of the answer. 
Result so far: 515.0
If we subtract 2100 from 2198, we get 98.
Append the next digit (8) from the dividend to 98 and continue with: 988 / 420

Going ahead to step 7:
When dividing 988 by 420, we get 2 with a remainder of 148.
Put 2 as the next digit of the answer. 
Result so far: 5152.0
If we subtract 840 from 988, we get 148.
Bring next digit (7) of the dividend behind the 148 and repeat the process: 1487 / 420

On to step 8:
1487 divided by 420 is 3 with a remainder of 227.
The next digit of our result is 3. 
Result so far: 51523.0
Subtracting 1260 from 1487 leaves us with 227.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2270, and continue the process.

Advancing to step 9:
When dividing 2270 by 420, we get 5 with a remainder of 170.
The number 5 becomes the next digit in our result. 
Result so far: 51523.5
If we take 2100 away from 2270, we end up with 170.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1700, and continue the process.

Step 10:
1700 divided by 420 is 4 with a remainder of 20.
Use 4 as the next digit of our solution. 
Result so far: 51523.54
Subtracting 1680 from 1700 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.

Moving on to step 11:
The number 420 fits into 200 0 times, leaving a remainder of 200.
The next digit of our result is 0. 
Result so far: 51523.54
Subtracting 0 from 200 leaves us with 200.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2000, and continue the process.

Moving on to step 12:
420 can be fit into 2000 4 times, resulting in a remainder of 320.
Use 4 as the next digit of our solution. 
Result so far: 51523.5404
If we subtract 1680 from 2000, we get 320.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3200, and continue the process.

Step 13:
420 can be fit into 3200 7 times, resulting in a remainder of 260.
Use 7 as the next digit of our solution. 
Result so far: 51523.54047
Subtracting 2940 from 3200 leaves us with 260.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2600, and continue the process.

Going ahead to step 14:
420 goes into 2600 6 times with a remainder of 80.
Put 6 as the next digit of the answer. 
Result so far: 51523.540476
If we take 2520 away from 2600, we end up with 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 800, and continue the process.

On to step 15:
420 can be fit into 800 1 times, resulting in a remainder of 380.
The next digit of our result is 1. 
Result so far: 51523.5404761
If we take 420 away from 800, we end up with 380.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3800, and continue the process.

Let's proceed to step 16:
If we divide 3800 by 420, we get 9 and a remainder of 20.
Use 9 as the next digit of our solution. 
Result so far: 51523.54047619
Deduct 3780 from 3800 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.

The final outcome is 51523.54047619, with a leftover of 2e-08.