721561 ÷ 39 
The aim is to understand the frequency of 39 in 721561.

On to step 1:
When dividing 7 by 39, we get 0 with a remainder of 7.
The next digit of our result is 0. 
Result so far: 0.0
The remainder is 7 after subtracting 0 from 7.
Include the next digit (2) from the dividend after 7, then repeat: 72 / 39

Let's proceed to step 2:
When dividing 72 by 39, we get 1 with a remainder of 33.
The next digit of our result is 1. 
Result so far: 1.0
If we subtract 39 from 72, we get 33.
Include the next digit (1) from the dividend after 33, then repeat: 331 / 39

Let's proceed to step 3:
If we divide 331 by 39, we get 8 and a remainder of 19.
The number 8 becomes the next digit in our result. 
Result so far: 18.0
Deduct 312 from 331 and we're left with 19.
Append the next digit (5) from the dividend to 19 and continue with: 195 / 39

Step 4:
195 divided by 39 is 5 with a remainder of 0.
Put 5 as the next digit of the answer. 
Result so far: 185.0
Deduct 195 from 195 and we're left with 0.
Bring next digit (6) of the dividend behind the 0 and repeat the process: 6 / 39

Advancing to step 5:
When dividing 6 by 39, we get 0 with a remainder of 6.
Use 0 as the next digit of our solution. 
Result so far: 1850.0
Subtracting 0 from 6 leaves us with 6.
Fetch the next digit (1) from the dividend, attach it to 6 and continue: 61 / 39

Let's proceed to step 6:
39 goes into 61 1 times with a remainder of 22.
Put 1 as the next digit of the answer. 
Result so far: 18501.0
Subtracting 39 from 61 leaves us with 22.
Since there are no more digits in the dividend, we add a zero to the remainder making it 220, and continue the process.

Step 7:
When dividing 220 by 39, we get 5 with a remainder of 25.
The next digit of our result is 5. 
Result so far: 18501.5
Deduct 195 from 220 and we're left with 25.
Since there are no more digits in the dividend, we add a zero to the remainder making it 250, and continue the process.

On to step 8:
39 can be fit into 250 6 times, resulting in a remainder of 16.
Put 6 as the next digit of the answer. 
Result so far: 18501.56
The remainder is 16 after subtracting 234 from 250.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Step 9:
The number 39 fits into 160 4 times, leaving a remainder of 4.
Use 4 as the next digit of our solution. 
Result so far: 18501.564
Deduct 156 from 160 and we're left with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Step 10:
When dividing 40 by 39, we get 1 with a remainder of 1.
Write down 1 as next digit of the result. 
Result so far: 18501.5641
The remainder is 1 after subtracting 39 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Advancing to step 11:
39 goes into 10 0 times with a remainder of 10.
The next digit of our result is 0. 
Result so far: 18501.5641
Subtract 0 from 10 to get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 12:
100 divided by 39 is 2 with a remainder of 22.
The next digit of our result is 2. 
Result so far: 18501.564102
Subtract 78 from 100 to get 22.
Since there are no more digits in the dividend, we add a zero to the remainder making it 220, and continue the process.

On to step 13:
39 can be fit into 220 5 times, resulting in a remainder of 25.
Write down 5 as next digit of the result. 
Result so far: 18501.5641025
If we take 195 away from 220, we end up with 25.
Since there are no more digits in the dividend, we add a zero to the remainder making it 250, and continue the process.

On to step 14:
39 goes into 250 6 times with a remainder of 16.
Put 6 as the next digit of the answer. 
Result so far: 18501.56410256
Deduct 234 from 250 and we're left with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Our division results in 18501.56410256 with a remaining 1.6e-08.