Let's divide 21517918 by 644
Let's see how many times 644 fits into 21517918.

Step 1:
When dividing 2 by 644, we get 0 with 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.
Include the next digit (1) from the dividend after 2, then repeat: 21 / 644

On to step 2:
644 can be fit into 21 0 times, resulting in a remainder of 21.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 21 and we're left with 21.
Append the next digit (5) from the dividend to 21 and continue with: 215 / 644

On to step 3:
215 divided by 644 is 0 with a remainder of 215.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 215 to get 215.
Bring next digit (1) of the dividend behind the 215 and repeat the process: 2151 / 644

Advancing to step 4:
644 goes into 2151 3 times with a remainder of 219.
Put 3 as the next digit of the answer. 
Result so far: 3.0
Subtracting 1932 from 2151 leaves us with 219.
Bring next digit (7) of the dividend behind the 219 and repeat the process: 2197 / 644

Let's proceed to step 5:
The number 644 fits into 2197 3 times, leaving a remainder of 265.
The next digit of our result is 3. 
Result so far: 33.0
Deduct 1932 from 2197 and we're left with 265.
Bring next digit (9) of the dividend behind the 265 and repeat the process: 2659 / 644

On to step 6:
2659 divided by 644 is 4 with a remainder of 83.
Record the quotient 4 as the next digit in the result. 
Result so far: 334.0
If we subtract 2576 from 2659, we get 83.
Bring next digit (1) of the dividend behind the 83 and repeat the process: 831 / 644

Step 7:
831 divided by 644 is 1 with a remainder of 187.
The number 1 becomes the next digit in our result. 
Result so far: 3341.0
If we take 644 away from 831, we end up with 187.
Append the next digit (8) from the dividend to 187 and continue with: 1878 / 644

Let's proceed to step 8:
644 goes into 1878 2 times with a remainder of 590.
Put 2 as the next digit of the answer. 
Result so far: 33412.0
If we take 1288 away from 1878, we end up with 590.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5900, and continue the process.

On to step 9:
644 goes into 5900 9 times with a remainder of 104.
The next digit of our result is 9. 
Result so far: 33412.9
Subtract 5796 from 5900 to get 104.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1040, and continue the process.

Moving on to step 10:
When dividing 1040 by 644, we get 1 with a remainder of 396.
Use 1 as the next digit of our solution. 
Result so far: 33412.91
If we subtract 644 from 1040, we get 396.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3960, and continue the process.

Moving on to step 11:
When dividing 3960 by 644, we get 6 with a remainder of 96.
Write down 6 as next digit of the result. 
Result so far: 33412.916
If we subtract 3864 from 3960, we get 96.
Since there are no more digits in the dividend, we add a zero to the remainder making it 960, and continue the process.

On to step 12:
644 can be fit into 960 1 times, resulting in a remainder of 316.
Write down 1 as next digit of the result. 
Result so far: 33412.9161
The remainder is 316 after subtracting 644 from 960.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3160, and continue the process.

Let's proceed to step 13:
3160 divided by 644 is 4 with a remainder of 584.
The next digit of our result is 4. 
Result so far: 33412.91614
Deduct 2576 from 3160 and we're left with 584.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5840, and continue the process.

Step 14:
When dividing 5840 by 644, we get 9 with a remainder of 44.
Use 9 as the next digit of our solution. 
Result so far: 33412.916149
The remainder is 44 after subtracting 5796 from 5840.
Since there are no more digits in the dividend, we add a zero to the remainder making it 440, and continue the process.

Going ahead to step 15:
The number 644 fits into 440 0 times, leaving a remainder of 440.
Use 0 as the next digit of our solution. 
Result so far: 33412.916149
Deduct 0 from 440 and we're left with 440.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4400, and continue the process.

Moving on to step 16:
When dividing 4400 by 644, we get 6 with a remainder of 536.
The number 6 becomes the next digit in our result. 
Result so far: 33412.91614906
The remainder is 536 after subtracting 3864 from 4400.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5360, and continue the process.

After the division, we end up with 33412.91614906 and a remainder of 5.36e-07.