754305 divided by 21 
The aim is to understand the frequency of 21 in 754305.

On to step 1:
When dividing 7 by 21, we get 0 with a remainder of 7.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 7 leaves us with 7.
Bring next digit (5) of the dividend behind the 7 and repeat the process: 75 / 21

Let's proceed to step 2:
75 divided by 21 is 3 with a remainder of 12.
The next digit of our result is 3. 
Result so far: 3.0
If we subtract 63 from 75, we get 12.
Include the next digit (4) from the dividend after 12, then repeat: 124 / 21

On to step 3:
The number 21 fits into 124 5 times, leaving a remainder of 19.
Use 5 as the next digit of our solution. 
Result so far: 35.0
If we subtract 105 from 124, we get 19.
Include the next digit (3) from the dividend after 19, then repeat: 193 / 21

Moving on to step 4:
21 can be fit into 193 9 times, resulting in a remainder of 4.
The next digit of our result is 9. 
Result so far: 359.0
If we take 189 away from 193, we end up with 4.
Append the next digit (0) from the dividend to 4 and continue with: 40 / 21

Step 5:
40 divided by 21 is 1 with a remainder of 19.
The next digit of our result is 1. 
Result so far: 3591.0
Subtract 21 from 40 to get 19.
Append the next digit (5) from the dividend to 19 and continue with: 195 / 21

Advancing to step 6:
The number 21 fits into 195 9 times, leaving a remainder of 6.
Put 9 as the next digit of the answer. 
Result so far: 35919.0
Deduct 189 from 195 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.

Step 7:
21 can be fit into 60 2 times, resulting in a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 35919.2
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:
180 divided by 21 is 8 with a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 35919.28
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.

Going ahead to step 9:
If we divide 120 by 21, we get 5 and a remainder of 15.
The next digit of our result is 5. 
Result so far: 35919.285
If we take 105 away from 120, we end up with 15.
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:
21 goes into 150 7 times with a remainder of 3.
Record the quotient 7 as the next digit in the result. 
Result so far: 35919.2857
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.

Moving on to step 11:
21 goes into 30 1 times with a remainder of 9.
Record the quotient 1 as the next digit in the result. 
Result so far: 35919.28571
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.

Advancing to step 12:
90 divided by 21 is 4 with a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 35919.285714
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.

Moving on to step 13:
If we divide 60 by 21, we get 2 and a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 35919.2857142
If we take 42 away from 60, we end up 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.

Going ahead to step 14:
When dividing 180 by 21, we get 8 with a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 35919.28571428
If we take 168 away from 180, we end up 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 final outcome is 35919.28571428, with a leftover of 1.2e-08.