80943563 divided by 21 
The aim is to understand the frequency of 21 in 80943563.

Advancing to step 1:
If we divide 8 by 21, we get 0 and a remainder of 8.
Write down 0 as next digit of the result. 
Result so far: 0.0
The remainder is 8 after subtracting 0 from 8.
Grab the next digit (0) from the dividend, add it to 8, then carry on: 80 / 21

Advancing to step 2:
21 goes into 80 3 times with a remainder of 17.
The next digit of our result is 3. 
Result so far: 3.0
Deduct 63 from 80 and we're left with 17.
Include the next digit (9) from the dividend after 17, then repeat: 179 / 21

Going ahead to step 3:
21 goes into 179 8 times with a remainder of 11.
The next digit of our result is 8. 
Result so far: 38.0
If we take 168 away from 179, we end up with 11.
Include the next digit (4) from the dividend after 11, then repeat: 114 / 21

Moving on to step 4:
21 can be fit into 114 5 times, resulting in a remainder of 9.
Record the quotient 5 as the next digit in the result. 
Result so far: 385.0
The remainder is 9 after subtracting 105 from 114.
Include the next digit (3) from the dividend after 9, then repeat: 93 / 21

Let's proceed to step 5:
21 goes into 93 4 times with a remainder of 9.
Put 4 as the next digit of the answer. 
Result so far: 3854.0
If we take 84 away from 93, we end up with 9.
Fetch the next digit (5) from the dividend, attach it to 9 and continue: 95 / 21

Advancing to step 6:
When dividing 95 by 21, we get 4 with a remainder of 11.
The next digit of our result is 4. 
Result so far: 38544.0
Deduct 84 from 95 and we're left with 11.
Append the next digit (6) from the dividend to 11 and continue with: 116 / 21

Step 7:
21 goes into 116 5 times with a remainder of 11.
Use 5 as the next digit of our solution. 
Result so far: 385445.0
The remainder is 11 after subtracting 105 from 116.
Bring next digit (3) of the dividend behind the 11 and repeat the process: 113 / 21

Step 8:
113 divided by 21 is 5 with a remainder of 8.
The next digit of our result is 5. 
Result so far: 3854455.0
Subtract 105 from 113 to get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Moving on to step 9:
If we divide 80 by 21, we get 3 and a remainder of 17.
Record the quotient 3 as the next digit in the result. 
Result so far: 3854455.3
If we subtract 63 from 80, we get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

On to step 10:
170 divided by 21 is 8 with a remainder of 2.
Put 8 as the next digit of the answer. 
Result so far: 3854455.38
If we take 168 away from 170, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Step 11:
If we divide 20 by 21, we get 0 and a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 3854455.38
Deduct 0 from 20 and we're left with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

On to step 12:
The number 21 fits into 200 9 times, leaving a remainder of 11.
Put 9 as the next digit of the answer. 
Result so far: 3854455.3809
Subtracting 189 from 200 leaves us with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Moving on to step 13:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Record the quotient 5 as the next digit in the result. 
Result so far: 3854455.38095
Subtracting 105 from 110 leaves us with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Moving on to step 14:
21 goes into 50 2 times with a remainder of 8.
The next digit of our result is 2. 
Result so far: 3854455.380952
Deduct 42 from 50 and we're left with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

On to step 15:
The number 21 fits into 80 3 times, leaving a remainder of 17.
Use 3 as the next digit of our solution. 
Result so far: 3854455.3809523
If we subtract 63 from 80, we get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Step 16:
If we divide 170 by 21, we get 8 and a remainder of 2.
The next digit of our result is 8. 
Result so far: 3854455.38095238
If we take 168 away from 170, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Our division results in 3854455.38095238 with a remaining 2e-09.