21507398 ÷ 648 
We want to figure out the number of times 21507398 can be divided by 648.

On to step 1:
648 can be fit into 2 0 times, resulting in a remainder of 2.
The next digit of our result is 0. 
Result so far: 0.0
Subtracting 0 from 2 leaves us with 2.
Grab the next digit (1) from the dividend, add it to 2, then carry on: 21 / 648

Advancing to step 2:
When dividing 21 by 648, we get 0 with a remainder of 21.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we subtract 0 from 21, we get 21.
Include the next digit (5) from the dividend after 21, then repeat: 215 / 648

Let's proceed to step 3:
215 divided by 648 is 0 with a remainder of 215.
Use 0 as the next digit of our solution. 
Result so far: 0.0
The remainder is 215 after subtracting 0 from 215.
Grab the next digit (0) from the dividend, add it to 215, then carry on: 2150 / 648

Advancing to step 4:
The number 648 fits into 2150 3 times, leaving a remainder of 206.
Put 3 as the next digit of the answer. 
Result so far: 3.0
Deduct 1944 from 2150 and we're left with 206.
Take the next digit (7) from the dividend and append it to 206, then repeat: 2067 / 648

Let's proceed to step 5:
648 can be fit into 2067 3 times, resulting in a remainder of 123.
The next digit of our result is 3. 
Result so far: 33.0
The remainder is 123 after subtracting 1944 from 2067.
Take the next digit (3) from the dividend and append it to 123, then repeat: 1233 / 648

Step 6:
648 can be fit into 1233 1 times, resulting in a remainder of 585.
The next digit of our result is 1. 
Result so far: 331.0
Deduct 648 from 1233 and we're left with 585.
Grab the next digit (9) from the dividend, add it to 585, then carry on: 5859 / 648

Going ahead to step 7:
When dividing 5859 by 648, we get 9 with a remainder of 27.
Put 9 as the next digit of the answer. 
Result so far: 3319.0
Deduct 5832 from 5859 and we're left with 27.
Fetch the next digit (8) from the dividend, attach it to 27 and continue: 278 / 648

On to step 8:
When dividing 278 by 648, we get 0 with a remainder of 278.
The next digit of our result is 0. 
Result so far: 33190.0
If we subtract 0 from 278, we get 278.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2780, and continue the process.

Going ahead to step 9:
648 goes into 2780 4 times with a remainder of 188.
Record the quotient 4 as the next digit in the result. 
Result so far: 33190.4
If we take 2592 away from 2780, we end up with 188.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1880, and continue the process.

Going ahead to step 10:
When dividing 1880 by 648, we get 2 with a remainder of 584.
Use 2 as the next digit of our solution. 
Result so far: 33190.42
If we subtract 1296 from 1880, we get 584.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5840, and continue the process.

On to step 11:
When dividing 5840 by 648, we get 9 with a remainder of 8.
Put 9 as the next digit of the answer. 
Result so far: 33190.429
Deduct 5832 from 5840 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.

Moving on to step 12:
When dividing 80 by 648, we get 0 with a remainder of 80.
The next digit of our result is 0. 
Result so far: 33190.429
If we take 0 away from 80, 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.

Step 13:
648 can be fit into 800 1 times, resulting in a remainder of 152.
Record the quotient 1 as the next digit in the result. 
Result so far: 33190.42901
Deduct 648 from 800 and we're left with 152.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1520, and continue the process.

On to step 14:
When dividing 1520 by 648, we get 2 with a remainder of 224.
Write down 2 as next digit of the result. 
Result so far: 33190.429012
Subtract 1296 from 1520 to get 224.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2240, and continue the process.

Moving on to step 15:
If we divide 2240 by 648, we get 3 and a remainder of 296.
Use 3 as the next digit of our solution. 
Result so far: 33190.4290123
Subtracting 1944 from 2240 leaves us with 296.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2960, and continue the process.

Moving on to step 16:
If we divide 2960 by 648, we get 4 and a remainder of 368.
The number 4 becomes the next digit in our result. 
Result so far: 33190.42901234
Subtract 2592 from 2960 to get 368.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3680, and continue the process.

The final result is 33190.42901234 with a remainder of 3.68e-07.