We're dividing 630290 by 21 
The aim is to understand the frequency of 21 in 630290.

Moving on to step 1:
The number 21 fits into 6 0 times, leaving a remainder of 6.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we subtract 0 from 6, we get 6.
Include the next digit (3) from the dividend after 6, then repeat: 63 / 21

On to step 2:
The number 21 fits into 63 3 times, leaving a remainder of 0.
Record the quotient 3 as the next digit in the result. 
Result so far: 3.0
Deduct 63 from 63 and we're left with 0.
Append the next digit (0) from the dividend to 0 and continue with: 0 / 21

On to step 3:
0 divided by 21 is 0 with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 30.0
Deduct 0 from 0 and we're left with 0.
Include the next digit (2) from the dividend after 0, then repeat: 2 / 21

Moving on to step 4:
21 goes into 2 0 times with a remainder of 2.
Use 0 as the next digit of our solution. 
Result so far: 300.0
Subtracting 0 from 2 leaves us with 2.
Include the next digit (9) from the dividend after 2, then repeat: 29 / 21

On to step 5:
If we divide 29 by 21, we get 1 and a remainder of 8.
Use 1 as the next digit of our solution. 
Result so far: 3001.0
If we take 21 away from 29, we end up with 8.
Include the next digit (0) from the dividend after 8, then repeat: 80 / 21

Step 6:
80 divided by 21 is 3 with a remainder of 17.
The number 3 becomes the next digit in our result. 
Result so far: 30013.0
If we take 63 away from 80, we end up 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.

Step 7:
The number 21 fits into 170 8 times, leaving a remainder of 2.
The next digit of our result is 8. 
Result so far: 30013.8
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.

Advancing to step 8:
21 can be fit into 20 0 times, resulting in a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 30013.8
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.

Moving on to step 9:
When dividing 200 by 21, we get 9 with a remainder of 11.
Put 9 as the next digit of the answer. 
Result so far: 30013.809
If we subtract 189 from 200, we 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.

On to step 10:
21 goes into 110 5 times with a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 30013.8095
Subtracting 105 from 110 leaves us 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.

On to step 11:
21 can be fit into 50 2 times, resulting in a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 30013.80952
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.

Going ahead to step 12:
21 goes into 80 3 times with a remainder of 17.
Write down 3 as next digit of the result. 
Result so far: 30013.809523
Deduct 63 from 80 and we're left 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.

Let's proceed to step 13:
If we divide 170 by 21, we get 8 and a remainder of 2.
The number 8 becomes the next digit in our result. 
Result so far: 30013.8095238
If we take 168 away from 170, we end up with 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 14:
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: 30013.8095238
Deduct 0 from 20 and we're left 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.

The final result is 30013.8095238 with a remainder of 2e-08.