We're dividing 453060 by 21 
The aim is to understand the frequency of 21 in 453060.

Let's proceed to step 1:
The number 21 fits into 4 0 times, leaving a remainder of 4.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 4, we end up with 4.
Fetch the next digit (5) from the dividend, attach it to 4 and continue: 45 / 21

Advancing to step 2:
21 goes into 45 2 times with a remainder of 3.
Put 2 as the next digit of the answer. 
Result so far: 2.0
Deduct 42 from 45 and we're left with 3.
Take the next digit (3) from the dividend and append it to 3, then repeat: 33 / 21

Step 3:
When dividing 33 by 21, we get 1 with a remainder of 12.
Record the quotient 1 as the next digit in the result. 
Result so far: 21.0
If we subtract 21 from 33, we get 12.
Append the next digit (0) from the dividend to 12 and continue with: 120 / 21

Going ahead to step 4:
21 goes into 120 5 times with a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 215.0
Subtracting 105 from 120 leaves us with 15.
Fetch the next digit (6) from the dividend, attach it to 15 and continue: 156 / 21

Step 5:
21 goes into 156 7 times with a remainder of 9.
Put 7 as the next digit of the answer. 
Result so far: 2157.0
Deduct 147 from 156 and we're left with 9.
Include the next digit (0) from the dividend after 9, then repeat: 90 / 21

On to step 6:
If we divide 90 by 21, we get 4 and a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 21574.0
Subtracting 84 from 90 leaves us 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.

Going ahead to step 7:
21 goes into 60 2 times with a remainder of 18.
Write down 2 as next digit of the result. 
Result so far: 21574.2
Deduct 42 from 60 and we're left 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.

Advancing to step 8:
21 goes into 180 8 times with a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 21574.28
Subtract 168 from 180 to 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 9:
21 goes into 120 5 times with a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 21574.285
The remainder is 15 after subtracting 105 from 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Step 10:
150 divided by 21 is 7 with a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 21574.2857
The remainder is 3 after subtracting 147 from 150.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Step 11:
If we divide 30 by 21, we get 1 and a remainder of 9.
The next digit of our result is 1. 
Result so far: 21574.28571
If we subtract 21 from 30, we 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.

Moving on to step 12:
If we divide 90 by 21, we get 4 and a remainder of 6.
The next digit of our result is 4. 
Result so far: 21574.285714
Deduct 84 from 90 and we're left 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.

Let's proceed to step 13:
21 can be fit into 60 2 times, resulting in a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 21574.2857142
Deduct 42 from 60 and we're left 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.

Let's proceed to step 14:
180 divided by 21 is 8 with a remainder of 12.
Put 8 as the next digit of the answer. 
Result so far: 21574.28571428
Subtracting 168 from 180 leaves us 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.

The quotient of the division is 21574.28571428, and the remainder is 1.2e-08.