We look at the division of 21348449 by 645 
The aim is to understand the frequency of 645 in 21348449.

Advancing to step 1:
When dividing 2 by 645, we get 0 with a remainder of 2.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
The remainder is 2 after subtracting 0 from 2.
Grab the next digit (1) from the dividend, add it to 2, then carry on: 21 / 645

Advancing to step 2:
21 divided by 645 is 0 with a remainder of 21.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 21 to get 21.
Fetch the next digit (3) from the dividend, attach it to 21 and continue: 213 / 645

Let's proceed to step 3:
The number 645 fits into 213 0 times, leaving a remainder of 213.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we subtract 0 from 213, we get 213.
Take the next digit (4) from the dividend and append it to 213, then repeat: 2134 / 645

Going ahead to step 4:
645 can be fit into 2134 3 times, resulting in a remainder of 199.
Record the quotient 3 as the next digit in the result. 
Result so far: 3.0
Deduct 1935 from 2134 and we're left with 199.
Fetch the next digit (8) from the dividend, attach it to 199 and continue: 1998 / 645

On to step 5:
If we divide 1998 by 645, we get 3 and a remainder of 63.
Record the quotient 3 as the next digit in the result. 
Result so far: 33.0
If we subtract 1935 from 1998, we get 63.
Take the next digit (4) from the dividend and append it to 63, then repeat: 634 / 645

Step 6:
645 can be fit into 634 0 times, resulting in a remainder of 634.
The number 0 becomes the next digit in our result. 
Result so far: 330.0
Subtracting 0 from 634 leaves us with 634.
Take the next digit (4) from the dividend and append it to 634, then repeat: 6344 / 645

Moving on to step 7:
645 goes into 6344 9 times with a remainder of 539.
The next digit of our result is 9. 
Result so far: 3309.0
If we take 5805 away from 6344, we end up with 539.
Take the next digit (9) from the dividend and append it to 539, then repeat: 5399 / 645

Let's proceed to step 8:
5399 divided by 645 is 8 with a remainder of 239.
Write down 8 as next digit of the result. 
Result so far: 33098.0
Deduct 5160 from 5399 and we're left with 239.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2390, and continue the process.

On to step 9:
If we divide 2390 by 645, we get 3 and a remainder of 455.
Write down 3 as next digit of the result. 
Result so far: 33098.3
Subtract 1935 from 2390 to get 455.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4550, and continue the process.

Going ahead to step 10:
645 can be fit into 4550 7 times, resulting in a remainder of 35.
Put 7 as the next digit of the answer. 
Result so far: 33098.37
If we subtract 4515 from 4550, we get 35.
Since there are no more digits in the dividend, we add a zero to the remainder making it 350, and continue the process.

Moving on to step 11:
The number 645 fits into 350 0 times, leaving a remainder of 350.
Use 0 as the next digit of our solution. 
Result so far: 33098.37
Subtracting 0 from 350 leaves us with 350.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3500, and continue the process.

Going ahead to step 12:
645 goes into 3500 5 times with a remainder of 275.
Write down 5 as next digit of the result. 
Result so far: 33098.3705
If we take 3225 away from 3500, we end up with 275.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2750, and continue the process.

Going ahead to step 13:
The number 645 fits into 2750 4 times, leaving a remainder of 170.
Put 4 as the next digit of the answer. 
Result so far: 33098.37054
If we take 2580 away from 2750, 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.

Advancing to step 14:
1700 divided by 645 is 2 with a remainder of 410.
The next digit of our result is 2. 
Result so far: 33098.370542
The remainder is 410 after subtracting 1290 from 1700.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4100, and continue the process.

On to step 15:
645 can be fit into 4100 6 times, resulting in a remainder of 230.
Use 6 as the next digit of our solution. 
Result so far: 33098.3705426
Subtracting 3870 from 4100 leaves us with 230.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2300, and continue the process.

Moving on to step 16:
645 can be fit into 2300 3 times, resulting in a remainder of 365.
Write down 3 as next digit of the result. 
Result so far: 33098.37054263
Subtract 1935 from 2300 to get 365.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3650, and continue the process.

Our division results in 33098.37054263 with a remaining 3.65e-07.