178233 divided by 21 
The aim is to understand the frequency of 21 in 178233.

Step 1:
1 divided by 21 is 0 with a remainder of 1.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we take 0 away from 1, we end up with 1.
Fetch the next digit (7) from the dividend, attach it to 1 and continue: 17 / 21

On to step 2:
17 divided by 21 is 0 with a remainder of 17.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we take 0 away from 17, we end up with 17.
Take the next digit (8) from the dividend and append it to 17, then repeat: 178 / 21

Going ahead to step 3:
If we divide 178 by 21, we get 8 and a remainder of 10.
Use 8 as the next digit of our solution. 
Result so far: 8.0
Subtracting 168 from 178 leaves us with 10.
Bring next digit (2) of the dividend behind the 10 and repeat the process: 102 / 21

Moving on to step 4:
21 goes into 102 4 times with a remainder of 18.
Record the quotient 4 as the next digit in the result. 
Result so far: 84.0
Subtract 84 from 102 to get 18.
Append the next digit (3) from the dividend to 18 and continue with: 183 / 21

Let's proceed to step 5:
If we divide 183 by 21, we get 8 and a remainder of 15.
Put 8 as the next digit of the answer. 
Result so far: 848.0
If we take 168 away from 183, we end up with 15.
Grab the next digit (3) from the dividend, add it to 15, then carry on: 153 / 21

On to step 6:
21 goes into 153 7 times with a remainder of 6.
Put 7 as the next digit of the answer. 
Result so far: 8487.0
The remainder is 6 after subtracting 147 from 153.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Advancing to step 7:
60 divided by 21 is 2 with a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 8487.2
Deduct 42 from 60 and we're left with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Moving on to step 8:
The number 21 fits into 180 8 times, leaving a remainder of 12.
The next digit of our result is 8. 
Result so far: 8487.28
Subtract 168 from 180 to get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Advancing to step 9:
21 goes into 120 5 times with a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 8487.285
If we take 105 away from 120, we end up with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Moving on to step 10:
21 can be fit into 150 7 times, resulting in a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 8487.2857
If we take 147 away from 150, we end up with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 11:
21 can be fit into 30 1 times, resulting in a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 8487.28571
The remainder is 9 after subtracting 21 from 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

On to step 12:
If we divide 90 by 21, we get 4 and a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 8487.285714
Deduct 84 from 90 and we're left with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Let's proceed to step 13:
If we divide 60 by 21, we get 2 and a remainder of 18.
Put 2 as the next digit of the answer. 
Result so far: 8487.2857142
If we subtract 42 from 60, we get 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Moving on to step 14:
180 divided by 21 is 8 with a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 8487.28571428
If we take 168 away from 180, we end up with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Our division results in 8487.28571428 with a remaining 1.2e-08.