We look at the division of 988458 by 21 
The aim is to understand the frequency of 21 in 988458.

Let's proceed to step 1:
9 divided by 21 is 0 with a remainder of 9.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 9, we get 9.
Grab the next digit (8) from the dividend, add it to 9, then carry on: 98 / 21

On to step 2:
If we divide 98 by 21, we get 4 and a remainder of 14.
Put 4 as the next digit of the answer. 
Result so far: 4.0
Subtract 84 from 98 to get 14.
Grab the next digit (8) from the dividend, add it to 14, then carry on: 148 / 21

Moving on to step 3:
21 can be fit into 148 7 times, resulting in a remainder of 1.
The number 7 becomes the next digit in our result. 
Result so far: 47.0
Subtract 147 from 148 to get 1.
Include the next digit (4) from the dividend after 1, then repeat: 14 / 21

Advancing to step 4:
If we divide 14 by 21, we get 0 and a remainder of 14.
Put 0 as the next digit of the answer. 
Result so far: 470.0
Subtract 0 from 14 to get 14.
Include the next digit (5) from the dividend after 14, then repeat: 145 / 21

Going ahead to step 5:
145 divided by 21 is 6 with a remainder of 19.
Record the quotient 6 as the next digit in the result. 
Result so far: 4706.0
The remainder is 19 after subtracting 126 from 145.
Grab the next digit (8) from the dividend, add it to 19, then carry on: 198 / 21

Advancing to step 6:
21 goes into 198 9 times with a remainder of 9.
Record the quotient 9 as the next digit in the result. 
Result so far: 47069.0
Subtract 189 from 198 to get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Advancing to step 7:
21 goes into 90 4 times with a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 47069.4
If we take 84 away from 90, we end up 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.

Step 8:
The number 21 fits into 60 2 times, leaving a remainder of 18.
The next digit of our result is 2. 
Result so far: 47069.42
Subtract 42 from 60 to 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.

Going ahead to step 9:
21 goes into 180 8 times with a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 47069.428
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.

Moving on to step 10:
120 divided by 21 is 5 with a remainder of 15.
Write down 5 as next digit of the result. 
Result so far: 47069.4285
Subtracting 105 from 120 leaves us 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 11:
21 can be fit into 150 7 times, resulting in a remainder of 3.
The number 7 becomes the next digit in our result. 
Result so far: 47069.42857
Subtracting 147 from 150 leaves us 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.

Step 12:
30 divided by 21 is 1 with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 47069.428571
Deduct 21 from 30 and we're left with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Going ahead to step 13:
When dividing 90 by 21, we get 4 with a remainder of 6.
The next digit of our result is 4. 
Result so far: 47069.4285714
If we take 84 away from 90, we end up 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.

Advancing to step 14:
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: 47069.42857142
If we take 42 away from 60, we end up 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.

In conclusion, the division gives 47069.42857142 with a balance of 1.8e-08.