609488 divided by 21 
The aim is to understand the frequency of 21 in 609488.

On to step 1:
If we divide 6 by 21, we get 0 and a remainder of 6.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 6 and we're left with 6.
Append the next digit (0) from the dividend to 6 and continue with: 60 / 21

Advancing to step 2:
The number 21 fits into 60 2 times, leaving a remainder of 18.
Put 2 as the next digit of the answer. 
Result so far: 2.0
The remainder is 18 after subtracting 42 from 60.
Bring next digit (9) of the dividend behind the 18 and repeat the process: 189 / 21

Advancing to step 3:
If we divide 189 by 21, we get 9 and a remainder of 0.
Record the quotient 9 as the next digit in the result. 
Result so far: 29.0
Subtract 189 from 189 to get 0.
Append the next digit (4) from the dividend to 0 and continue with: 4 / 21

Advancing to step 4:
21 can be fit into 4 0 times, resulting in a remainder of 4.
Put 0 as the next digit of the answer. 
Result so far: 290.0
Subtract 0 from 4 to get 4.
Grab the next digit (8) from the dividend, add it to 4, then carry on: 48 / 21

Advancing to step 5:
If we divide 48 by 21, we get 2 and a remainder of 6.
Put 2 as the next digit of the answer. 
Result so far: 2902.0
Subtract 42 from 48 to get 6.
Grab the next digit (8) from the dividend, add it to 6, then carry on: 68 / 21

Step 6:
21 can be fit into 68 3 times, resulting in a remainder of 5.
The next digit of our result is 3. 
Result so far: 29023.0
The remainder is 5 after subtracting 63 from 68.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Step 7:
21 goes into 50 2 times with a remainder of 8.
Write down 2 as next digit of the result. 
Result so far: 29023.2
Subtracting 42 from 50 leaves us with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Step 8:
The number 21 fits into 80 3 times, leaving a remainder of 17.
The number 3 becomes the next digit in our result. 
Result so far: 29023.23
Subtracting 63 from 80 leaves us with 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Moving on to step 9:
When dividing 170 by 21, we get 8 with a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 29023.238
Subtract 168 from 170 to 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.

Let's proceed to step 10:
21 can be fit into 20 0 times, resulting in a remainder of 20.
Put 0 as the next digit of the answer. 
Result so far: 29023.238
If we take 0 away from 20, we end up with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Step 11:
If we divide 200 by 21, we get 9 and a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 29023.23809
Subtract 189 from 200 to get 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 12:
21 can be fit into 110 5 times, resulting in a remainder of 5.
The next digit of our result is 5. 
Result so far: 29023.238095
Subtract 105 from 110 to get 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Going ahead to step 13:
If we divide 50 by 21, we get 2 and a remainder of 8.
The next digit of our result is 2. 
Result so far: 29023.2380952
Subtracting 42 from 50 leaves us with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Advancing to step 14:
80 divided by 21 is 3 with a remainder of 17.
Use 3 as the next digit of our solution. 
Result so far: 29023.23809523
Subtract 63 from 80 to get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

The final result is 29023.23809523 with a remainder of 1.7e-08.