We look at the division of 418289 by 21 
The aim is to understand the frequency of 21 in 418289.

Moving on to step 1:
4 divided by 21 is 0 with a remainder of 4.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 4 and we're left with 4.
Fetch the next digit (1) from the dividend, attach it to 4 and continue: 41 / 21

On to step 2:
If we divide 41 by 21, we get 1 and a remainder of 20.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
Subtracting 21 from 41 leaves us with 20.
Bring next digit (8) of the dividend behind the 20 and repeat the process: 208 / 21

On to step 3:
The number 21 fits into 208 9 times, leaving a remainder of 19.
Write down 9 as next digit of the result. 
Result so far: 19.0
Deduct 189 from 208 and we're left with 19.
Bring next digit (2) of the dividend behind the 19 and repeat the process: 192 / 21

Moving on to step 4:
192 divided by 21 is 9 with a remainder of 3.
Put 9 as the next digit of the answer. 
Result so far: 199.0
If we take 189 away from 192, we end up with 3.
Grab the next digit (8) from the dividend, add it to 3, then carry on: 38 / 21

Step 5:
If we divide 38 by 21, we get 1 and a remainder of 17.
Use 1 as the next digit of our solution. 
Result so far: 1991.0
The remainder is 17 after subtracting 21 from 38.
Take the next digit (9) from the dividend and append it to 17, then repeat: 179 / 21

Let's proceed to step 6:
When dividing 179 by 21, we get 8 with a remainder of 11.
Use 8 as the next digit of our solution. 
Result so far: 19918.0
The remainder is 11 after subtracting 168 from 179.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

On to step 7:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Put 5 as the next digit of the answer. 
Result so far: 19918.5
If we take 105 away from 110, we end up 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.

Advancing to step 8:
The number 21 fits into 50 2 times, leaving a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 19918.52
Subtract 42 from 50 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.

On to step 9:
21 goes into 80 3 times with a remainder of 17.
The number 3 becomes the next digit in our result. 
Result so far: 19918.523
The remainder is 17 after subtracting 63 from 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Step 10:
The number 21 fits into 170 8 times, leaving a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 19918.5238
If we subtract 168 from 170, we get 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:
20 divided by 21 is 0 with a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 19918.5238
Subtract 0 from 20 to get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Going ahead to step 12:
200 divided by 21 is 9 with a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 19918.523809
If we take 189 away from 200, we end up 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:
110 divided by 21 is 5 with a remainder of 5.
The number 5 becomes the next digit in our result. 
Result so far: 19918.5238095
Deduct 105 from 110 and we're left 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.

Advancing to step 14:
The number 21 fits into 50 2 times, leaving a remainder of 8.
The next digit of our result is 2. 
Result so far: 19918.52380952
If we subtract 42 from 50, we 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.

The final result is 19918.52380952 with a remainder of 8e-09.