We look at the division of 21720813 by 609 
The aim is to understand the frequency of 609 in 21720813.

Let's proceed to step 1:
609 can be fit into 2 0 times, resulting in a remainder of 2.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we subtract 0 from 2, we get 2.
Fetch the next digit (1) from the dividend, attach it to 2 and continue: 21 / 609

Step 2:
When dividing 21 by 609, we get 0 with a remainder of 21.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
The remainder is 21 after subtracting 0 from 21.
Include the next digit (7) from the dividend after 21, then repeat: 217 / 609

Going ahead to step 3:
The number 609 fits into 217 0 times, leaving a remainder of 217.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtract 0 from 217 to get 217.
Grab the next digit (2) from the dividend, add it to 217, then carry on: 2172 / 609

On to step 4:
When dividing 2172 by 609, we get 3 with a remainder of 345.
The number 3 becomes the next digit in our result. 
Result so far: 3.0
Subtracting 1827 from 2172 leaves us with 345.
Bring next digit (0) of the dividend behind the 345 and repeat the process: 3450 / 609

Advancing to step 5:
The number 609 fits into 3450 5 times, leaving a remainder of 405.
Record the quotient 5 as the next digit in the result. 
Result so far: 35.0
Deduct 3045 from 3450 and we're left with 405.
Append the next digit (8) from the dividend to 405 and continue with: 4058 / 609

Advancing to step 6:
609 goes into 4058 6 times with a remainder of 404.
Record the quotient 6 as the next digit in the result. 
Result so far: 356.0
The remainder is 404 after subtracting 3654 from 4058.
Include the next digit (1) from the dividend after 404, then repeat: 4041 / 609

Advancing to step 7:
When dividing 4041 by 609, we get 6 with a remainder of 387.
Record the quotient 6 as the next digit in the result. 
Result so far: 3566.0
Subtracting 3654 from 4041 leaves us with 387.
Fetch the next digit (3) from the dividend, attach it to 387 and continue: 3873 / 609

Going ahead to step 8:
3873 divided by 609 is 6 with a remainder of 219.
The next digit of our result is 6. 
Result so far: 35666.0
Subtracting 3654 from 3873 leaves us with 219.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2190, and continue the process.

Advancing to step 9:
The number 609 fits into 2190 3 times, leaving a remainder of 363.
Use 3 as the next digit of our solution. 
Result so far: 35666.3
Subtract 1827 from 2190 to get 363.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3630, and continue the process.

Advancing to step 10:
609 can be fit into 3630 5 times, resulting in a remainder of 585.
Record the quotient 5 as the next digit in the result. 
Result so far: 35666.35
Subtract 3045 from 3630 to get 585.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5850, and continue the process.

Moving on to step 11:
609 can be fit into 5850 9 times, resulting in a remainder of 369.
Put 9 as the next digit of the answer. 
Result so far: 35666.359
The remainder is 369 after subtracting 5481 from 5850.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3690, and continue the process.

Step 12:
When dividing 3690 by 609, we get 6 with a remainder of 36.
The number 6 becomes the next digit in our result. 
Result so far: 35666.3596
If we subtract 3654 from 3690, we get 36.
Since there are no more digits in the dividend, we add a zero to the remainder making it 360, and continue the process.

Let's proceed to step 13:
When dividing 360 by 609, we get 0 with a remainder of 360.
Use 0 as the next digit of our solution. 
Result so far: 35666.3596
Subtracting 0 from 360 leaves us with 360.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3600, and continue the process.

On to step 14:
When dividing 3600 by 609, we get 5 with a remainder of 555.
Put 5 as the next digit of the answer. 
Result so far: 35666.359605
If we take 3045 away from 3600, we end up with 555.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5550, and continue the process.

Advancing to step 15:
609 goes into 5550 9 times with a remainder of 69.
The next digit of our result is 9. 
Result so far: 35666.3596059
The remainder is 69 after subtracting 5481 from 5550.
Since there are no more digits in the dividend, we add a zero to the remainder making it 690, and continue the process.

Advancing to step 16:
When dividing 690 by 609, we get 1 with a remainder of 81.
Write down 1 as next digit of the result. 
Result so far: 35666.35960591
Deduct 609 from 690 and we're left with 81.
Since there are no more digits in the dividend, we add a zero to the remainder making it 810, and continue the process.

After the division, we end up with 35666.35960591 and a remainder of 8.1e-08.