251631 ÷ 81 
The aim is to understand the frequency of 81 in 251631.

On to step 1:
81 goes into 2 0 times with a remainder of 2.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtract 0 from 2 to get 2.
Bring next digit (5) of the dividend behind the 2 and repeat the process: 25 / 81

Let's proceed to step 2:
When dividing 25 by 81, we get 0 with a remainder of 25.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 25, we get 25.
Append the next digit (1) from the dividend to 25 and continue with: 251 / 81

Advancing to step 3:
81 can be fit into 251 3 times, resulting in a remainder of 8.
The next digit of our result is 3. 
Result so far: 3.0
Deduct 243 from 251 and we're left with 8.
Take the next digit (6) from the dividend and append it to 8, then repeat: 86 / 81

Step 4:
The number 81 fits into 86 1 times, leaving a remainder of 5.
Use 1 as the next digit of our solution. 
Result so far: 31.0
If we take 81 away from 86, we end up with 5.
Fetch the next digit (3) from the dividend, attach it to 5 and continue: 53 / 81

Going ahead to step 5:
81 can be fit into 53 0 times, resulting in a remainder of 53.
Record the quotient 0 as the next digit in the result. 
Result so far: 310.0
If we take 0 away from 53, we end up with 53.
Take the next digit (1) from the dividend and append it to 53, then repeat: 531 / 81

Let's proceed to step 6:
81 can be fit into 531 6 times, resulting in a remainder of 45.
Write down 6 as next digit of the result. 
Result so far: 3106.0
Deduct 486 from 531 and we're left with 45.
Since there are no more digits in the dividend, we add a zero to the remainder making it 450, and continue the process.

Let's proceed to step 7:
450 divided by 81 is 5 with a remainder of 45.
The number 5 becomes the next digit in our result. 
Result so far: 3106.5
Deduct 405 from 450 and we're left with 45.
Since there are no more digits in the dividend, we add a zero to the remainder making it 450, and continue the process.

Step 8:
If we divide 450 by 81, we get 5 and a remainder of 45.
Record the quotient 5 as the next digit in the result. 
Result so far: 3106.55
If we subtract 405 from 450, we get 45.
Since there are no more digits in the dividend, we add a zero to the remainder making it 450, and continue the process.

The final result is 3106.55 with a remainder of 0.045.