43871221 divided by 81 
The aim is to understand the frequency of 81 in 43871221.

On to step 1:
81 goes into 4 0 times with a remainder of 4.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 4 and we're left with 4.
Bring next digit (3) of the dividend behind the 4 and repeat the process: 43 / 81

On to step 2:
When dividing 43 by 81, we get 0 with a remainder of 43.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtract 0 from 43 to get 43.
Include the next digit (8) from the dividend after 43, then repeat: 438 / 81

Let's proceed to step 3:
When dividing 438 by 81, we get 5 with a remainder of 33.
Record the quotient 5 as the next digit in the result. 
Result so far: 5.0
If we take 405 away from 438, we end up with 33.
Bring next digit (7) of the dividend behind the 33 and repeat the process: 337 / 81

Advancing to step 4:
337 divided by 81 is 4 with a remainder of 13.
Record the quotient 4 as the next digit in the result. 
Result so far: 54.0
The remainder is 13 after subtracting 324 from 337.
Bring next digit (1) of the dividend behind the 13 and repeat the process: 131 / 81

Going ahead to step 5:
131 divided by 81 is 1 with a remainder of 50.
Use 1 as the next digit of our solution. 
Result so far: 541.0
The remainder is 50 after subtracting 81 from 131.
Take the next digit (2) from the dividend and append it to 50, then repeat: 502 / 81

On to step 6:
81 can be fit into 502 6 times, resulting in a remainder of 16.
Write down 6 as next digit of the result. 
Result so far: 5416.0
Subtracting 486 from 502 leaves us with 16.
Bring next digit (2) of the dividend behind the 16 and repeat the process: 162 / 81

Step 7:
When dividing 162 by 81, we get 2 with a remainder of 0.
Write down 2 as next digit of the result. 
Result so far: 54162.0
Subtracting 162 from 162 leaves us with 0.
Bring next digit (1) of the dividend behind the 0 and repeat the process: 1 / 81

Moving on to step 8:
81 goes into 1 0 times with a remainder of 1.
Put 0 as the next digit of the answer. 
Result so far: 541620.0
Subtract 0 from 1 to get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Step 9:
If we divide 10 by 81, we get 0 and a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 541620.0
Deduct 0 from 10 and we're left with 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 10:
When dividing 100 by 81, we get 1 with a remainder of 19.
The number 1 becomes the next digit in our result. 
Result so far: 541620.01
If we take 81 away from 100, we end up with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Advancing to step 11:
190 divided by 81 is 2 with a remainder of 28.
Record the quotient 2 as the next digit in the result. 
Result so far: 541620.012
The remainder is 28 after subtracting 162 from 190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 280, and continue the process.

Advancing to step 12:
When dividing 280 by 81, we get 3 with a remainder of 37.
Use 3 as the next digit of our solution. 
Result so far: 541620.0123
If we take 243 away from 280, we end up with 37.
Since there are no more digits in the dividend, we add a zero to the remainder making it 370, and continue the process.

Advancing to step 13:
The number 81 fits into 370 4 times, leaving a remainder of 46.
The next digit of our result is 4. 
Result so far: 541620.01234
Subtract 324 from 370 to get 46.
Since there are no more digits in the dividend, we add a zero to the remainder making it 460, and continue the process.

Step 14:
81 goes into 460 5 times with a remainder of 55.
Record the quotient 5 as the next digit in the result. 
Result so far: 541620.012345
If we take 405 away from 460, we end up with 55.
Since there are no more digits in the dividend, we add a zero to the remainder making it 550, and continue the process.

Let's proceed to step 15:
81 goes into 550 6 times with a remainder of 64.
The next digit of our result is 6. 
Result so far: 541620.0123456
If we subtract 486 from 550, we get 64.
Since there are no more digits in the dividend, we add a zero to the remainder making it 640, and continue the process.

On to step 16:
The number 81 fits into 640 7 times, leaving a remainder of 73.
Put 7 as the next digit of the answer. 
Result so far: 541620.01234567
Subtracting 567 from 640 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.

After the division, we end up with 541620.01234567 and a remainder of 7.3e-08.