We divide 513521 by 1
The aim is to understand the frequency of 1 in 513521.

Advancing to step 1:
The number 1 fits into 5 5 times, leaving a remainder of 0.
Put 5 as the next digit of the answer. 
Result so far: 5.0
If we take 5 away from 5, we end up with 0.
Grab the next digit (1) from the dividend, add it to 0, then carry on: 1 / 1

Moving on to step 2:
The number 1 fits into 1 1 times, leaving a remainder of 0.
Record the quotient 1 as the next digit in the result. 
Result so far: 51.0
Deduct 1 from 1 and we're left with 0.
Include the next digit (3) from the dividend after 0, then repeat: 3 / 1

Step 3:
1 goes into 3 3 times with a remainder of 0.
The number 3 becomes the next digit in our result. 
Result so far: 513.0
Subtracting 3 from 3 leaves us with 0.
Take the next digit (5) from the dividend and append it to 0, then repeat: 5 / 1

Moving on to step 4:
When dividing 5 by 1, we get 5 with a remainder of 0.
Write down 5 as next digit of the result. 
Result so far: 5135.0
If we subtract 5 from 5, we get 0.
Bring next digit (2) of the dividend behind the 0 and repeat the process: 2 / 1

Let's proceed to step 5:
The number 1 fits into 2 2 times, leaving a remainder of 0.
Put 2 as the next digit of the answer. 
Result so far: 51352.0
Subtracting 2 from 2 leaves us with 0.
Append the next digit (1) from the dividend to 0 and continue with: 1 / 1

Going ahead to step 6:
When dividing 1 by 1, we get 1 with a remainder of 0.
Put 1 as the next digit of the answer. 
Result so far: 513521.0
If we take 1 away from 1, we end up with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Step 7:
1 goes into 0 0 times with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 513521.0
Subtract 0 from 0 to get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Let's proceed to step 8:
0 divided by 1 is 0 with a remainder of 0.
The number 0 becomes the next digit in our result. 
Result so far: 513521.0
If we subtract 0 from 0, we get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

After the division, we end up with 513521.0 and a remainder of 0.0.