We look at the division of 998490 by 21 
The aim is to understand the frequency of 21 in 998490.

Advancing to step 1:
21 goes into 9 0 times with a remainder of 9.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we take 0 away from 9, we end up with 9.
Take the next digit (9) from the dividend and append it to 9, then repeat: 99 / 21

Let's proceed to step 2:
99 divided by 21 is 4 with a remainder of 15.
Use 4 as the next digit of our solution. 
Result so far: 4.0
The remainder is 15 after subtracting 84 from 99.
Include the next digit (8) from the dividend after 15, then repeat: 158 / 21

On to step 3:
158 divided by 21 is 7 with a remainder of 11.
The next digit of our result is 7. 
Result so far: 47.0
Deduct 147 from 158 and we're left with 11.
Append the next digit (4) from the dividend to 11 and continue with: 114 / 21

Step 4:
The number 21 fits into 114 5 times, leaving a remainder of 9.
The next digit of our result is 5. 
Result so far: 475.0
If we subtract 105 from 114, we get 9.
Append the next digit (9) from the dividend to 9 and continue with: 99 / 21

Going ahead to step 5:
The number 21 fits into 99 4 times, leaving a remainder of 15.
Write down 4 as next digit of the result. 
Result so far: 4754.0
Subtract 84 from 99 to get 15.
Append the next digit (0) from the dividend to 15 and continue with: 150 / 21

On to step 6:
When dividing 150 by 21, we get 7 with a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 47547.0
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.

On to step 7:
21 goes into 30 1 times with a remainder of 9.
The next digit of our result is 1. 
Result so far: 47547.1
If we take 21 away from 30, we end up 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 8:
21 goes into 90 4 times with a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 47547.14
The remainder is 6 after subtracting 84 from 90.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Step 9:
When dividing 60 by 21, we get 2 with a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 47547.142
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 10:
If we divide 180 by 21, we get 8 and a remainder of 12.
Put 8 as the next digit of the answer. 
Result so far: 47547.1428
If we subtract 168 from 180, we 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.

On to step 11:
If we divide 120 by 21, we get 5 and a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 47547.14285
Subtract 105 from 120 to get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Advancing to step 12:
When dividing 150 by 21, we get 7 with a remainder of 3.
The next digit of our result is 7. 
Result so far: 47547.142857
Deduct 147 from 150 and we're left 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.

On to step 13:
If we divide 30 by 21, we get 1 and a remainder of 9.
Record the quotient 1 as the next digit in the result. 
Result so far: 47547.1428571
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.

Let's proceed to step 14:
When dividing 90 by 21, we get 4 with a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 47547.14285714
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.

The quotient of the division is 47547.14285714, and the remainder is 6e-09.