We look at the division of 17215879 by 123 
The aim is to understand the frequency of 123 in 17215879.

On to step 1:
The number 123 fits into 1 0 times, leaving a remainder of 1.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtract 0 from 1 to get 1.
Include the next digit (7) from the dividend after 1, then repeat: 17 / 123

Let's proceed to step 2:
123 can be fit into 17 0 times, resulting in a remainder of 17.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 17 and we're left with 17.
Grab the next digit (2) from the dividend, add it to 17, then carry on: 172 / 123

Moving on to step 3:
If we divide 172 by 123, we get 1 and a remainder of 49.
Write down 1 as next digit of the result. 
Result so far: 1.0
If we subtract 123 from 172, we get 49.
Grab the next digit (1) from the dividend, add it to 49, then carry on: 491 / 123

Step 4:
If we divide 491 by 123, we get 3 and a remainder of 122.
The next digit of our result is 3. 
Result so far: 13.0
If we take 369 away from 491, we end up with 122.
Bring next digit (5) of the dividend behind the 122 and repeat the process: 1225 / 123

On to step 5:
1225 divided by 123 is 9 with a remainder of 118.
The number 9 becomes the next digit in our result. 
Result so far: 139.0
If we subtract 1107 from 1225, we get 118.
Append the next digit (8) from the dividend to 118 and continue with: 1188 / 123

Going ahead to step 6:
1188 divided by 123 is 9 with a remainder of 81.
Use 9 as the next digit of our solution. 
Result so far: 1399.0
If we take 1107 away from 1188, we end up with 81.
Fetch the next digit (7) from the dividend, attach it to 81 and continue: 817 / 123

Step 7:
817 divided by 123 is 6 with a remainder of 79.
The next digit of our result is 6. 
Result so far: 13996.0
Subtract 738 from 817 to get 79.
Include the next digit (9) from the dividend after 79, then repeat: 799 / 123

Let's proceed to step 8:
When dividing 799 by 123, we get 6 with a remainder of 61.
The number 6 becomes the next digit in our result. 
Result so far: 139966.0
Deduct 738 from 799 and we're left with 61.
Since there are no more digits in the dividend, we add a zero to the remainder making it 610, and continue the process.

Advancing to step 9:
123 goes into 610 4 times with a remainder of 118.
The number 4 becomes the next digit in our result. 
Result so far: 139966.4
If we subtract 492 from 610, we get 118.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1180, and continue the process.

Moving on to step 10:
The number 123 fits into 1180 9 times, leaving a remainder of 73.
Write down 9 as next digit of the result. 
Result so far: 139966.49
If we take 1107 away from 1180, we end up with 73.
Since there are no more digits in the dividend, we add a zero to the remainder making it 730, and continue the process.

Moving on to step 11:
730 divided by 123 is 5 with a remainder of 115.
Record the quotient 5 as the next digit in the result. 
Result so far: 139966.495
The remainder is 115 after subtracting 615 from 730.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1150, and continue the process.

Advancing to step 12:
1150 divided by 123 is 9 with a remainder of 43.
Record the quotient 9 as the next digit in the result. 
Result so far: 139966.4959
If we subtract 1107 from 1150, we get 43.
Since there are no more digits in the dividend, we add a zero to the remainder making it 430, and continue the process.

Step 13:
If we divide 430 by 123, we get 3 and a remainder of 61.
Write down 3 as next digit of the result. 
Result so far: 139966.49593
Subtract 369 from 430 to get 61.
Since there are no more digits in the dividend, we add a zero to the remainder making it 610, and continue the process.

Advancing to step 14:
123 goes into 610 4 times with a remainder of 118.
Record the quotient 4 as the next digit in the result. 
Result so far: 139966.495934
The remainder is 118 after subtracting 492 from 610.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1180, and continue the process.

Step 15:
123 goes into 1180 9 times with a remainder of 73.
Record the quotient 9 as the next digit in the result. 
Result so far: 139966.4959349
Subtracting 1107 from 1180 leaves us with 73.
Since there are no more digits in the dividend, we add a zero to the remainder making it 730, and continue the process.

Let's proceed to step 16:
730 divided by 123 is 5 with a remainder of 115.
The number 5 becomes the next digit in our result. 
Result so far: 139966.49593495
Subtracting 615 from 730 leaves us with 115.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1150, and continue the process.

After the division, we end up with 139966.49593495 and a remainder of 1.15e-07.