125923 divided by 21 
The aim is to understand the frequency of 21 in 125923.

Step 1:
If we divide 1 by 21, we get 0 and a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 1 and we're left with 1.
Grab the next digit (2) from the dividend, add it to 1, then carry on: 12 / 21

Moving on to step 2:
21 goes into 12 0 times with a remainder of 12.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtracting 0 from 12 leaves us with 12.
Grab the next digit (5) from the dividend, add it to 12, then carry on: 125 / 21

Going ahead to step 3:
21 can be fit into 125 5 times, resulting in a remainder of 20.
Write down 5 as next digit of the result. 
Result so far: 5.0
Deduct 105 from 125 and we're left with 20.
Append the next digit (9) from the dividend to 20 and continue with: 209 / 21

Let's proceed to step 4:
21 can be fit into 209 9 times, resulting in a remainder of 20.
Write down 9 as next digit of the result. 
Result so far: 59.0
If we subtract 189 from 209, we get 20.
Grab the next digit (2) from the dividend, add it to 20, then carry on: 202 / 21

Let's proceed to step 5:
21 goes into 202 9 times with a remainder of 13.
The number 9 becomes the next digit in our result. 
Result so far: 599.0
If we subtract 189 from 202, we get 13.
Append the next digit (3) from the dividend to 13 and continue with: 133 / 21

Let's proceed to step 6:
21 can be fit into 133 6 times, resulting in a remainder of 7.
Use 6 as the next digit of our solution. 
Result so far: 5996.0
Deduct 126 from 133 and we're left with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

On to step 7:
21 can be fit into 70 3 times, resulting in a remainder of 7.
Put 3 as the next digit of the answer. 
Result so far: 5996.3
The remainder is 7 after subtracting 63 from 70.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

On to step 8:
21 goes into 70 3 times with a remainder of 7.
The next digit of our result is 3. 
Result so far: 5996.33
Subtracting 63 from 70 leaves us with 7.
Since there are no more digits in the dividend, we add a zero to the remainder making it 70, and continue the process.

In conclusion, the division gives 5996.33 with a balance of 0.007.