21815513 ÷ 39 
We want to figure out the number of times 21815513 can be divided by 39.

Let's proceed to step 1:
When dividing 2 by 39, we get 0 with a remainder of 2.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 2, we end up with 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 39

Step 2:
39 can be fit into 21 0 times, resulting in a remainder of 21.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtract 0 from 21 to get 21.
Take the next digit (8) from the dividend and append it to 21, then repeat: 218 / 39

On to step 3:
39 can be fit into 218 5 times, resulting in a remainder of 23.
The number 5 becomes the next digit in our result. 
Result so far: 5.0
Deduct 195 from 218 and we're left with 23.
Fetch the next digit (1) from the dividend, attach it to 23 and continue: 231 / 39

Moving on to step 4:
When dividing 231 by 39, we get 5 with a remainder of 36.
Put 5 as the next digit of the answer. 
Result so far: 55.0
The remainder is 36 after subtracting 195 from 231.
Bring next digit (5) of the dividend behind the 36 and repeat the process: 365 / 39

Step 5:
39 goes into 365 9 times with a remainder of 14.
Put 9 as the next digit of the answer. 
Result so far: 559.0
Deduct 351 from 365 and we're left with 14.
Fetch the next digit (5) from the dividend, attach it to 14 and continue: 145 / 39

Step 6:
When dividing 145 by 39, we get 3 with a remainder of 28.
The next digit of our result is 3. 
Result so far: 5593.0
If we subtract 117 from 145, we get 28.
Fetch the next digit (1) from the dividend, attach it to 28 and continue: 281 / 39

On to step 7:
If we divide 281 by 39, we get 7 and a remainder of 8.
The number 7 becomes the next digit in our result. 
Result so far: 55937.0
The remainder is 8 after subtracting 273 from 281.
Bring next digit (3) of the dividend behind the 8 and repeat the process: 83 / 39

Let's proceed to step 8:
When dividing 83 by 39, we get 2 with a remainder of 5.
Put 2 as the next digit of the answer. 
Result so far: 559372.0
Deduct 78 from 83 and we're left 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.

Step 9:
50 divided by 39 is 1 with a remainder of 11.
Use 1 as the next digit of our solution. 
Result so far: 559372.1
Subtracting 39 from 50 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.

Advancing to step 10:
The number 39 fits into 110 2 times, leaving a remainder of 32.
The number 2 becomes the next digit in our result. 
Result so far: 559372.12
Subtract 78 from 110 to get 32.
Since there are no more digits in the dividend, we add a zero to the remainder making it 320, and continue the process.

Advancing to step 11:
When dividing 320 by 39, we get 8 with a remainder of 8.
Use 8 as the next digit of our solution. 
Result so far: 559372.128
The remainder is 8 after subtracting 312 from 320.
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:
If we divide 80 by 39, we get 2 and a remainder of 2.
Record the quotient 2 as the next digit in the result. 
Result so far: 559372.1282
If we subtract 78 from 80, 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.

Going ahead to step 13:
When dividing 20 by 39, we get 0 with a remainder of 20.
Put 0 as the next digit of the answer. 
Result so far: 559372.1282
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.

Moving on to step 14:
The number 39 fits into 200 5 times, leaving a remainder of 5.
Use 5 as the next digit of our solution. 
Result so far: 559372.128205
If we subtract 195 from 200, we get 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Moving on to step 15:
39 goes into 50 1 times with a remainder of 11.
Record the quotient 1 as the next digit in the result. 
Result so far: 559372.1282051
Subtract 39 from 50 to get 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Advancing to step 16:
39 goes into 110 2 times with a remainder of 32.
Put 2 as the next digit of the answer. 
Result so far: 559372.12820512
Deduct 78 from 110 and we're left with 32.
Since there are no more digits in the dividend, we add a zero to the remainder making it 320, and continue the process.

The final outcome is 559372.12820512, with a leftover of 3.2e-08.