We divide 412509 by 21
The aim is to understand the frequency of 21 in 412509.

Step 1:
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: 0.0
If we subtract 0 from 4, we get 4.
Fetch the next digit (1) from the dividend, attach it to 4 and continue: 41 / 21

Moving on to step 2:
When dividing 41 by 21, we get 1 with a remainder of 20.
The next digit of our result is 1. 
Result so far: 1.0
If we take 21 away from 41, we end up with 20.
Bring next digit (2) of the dividend behind the 20 and repeat the process: 202 / 21

On to step 3:
When dividing 202 by 21, we get 9 with a remainder of 13.
Put 9 as the next digit of the answer. 
Result so far: 19.0
Subtract 189 from 202 to get 13.
Take the next digit (5) from the dividend and append it to 13, then repeat: 135 / 21

Advancing to step 4:
135 divided by 21 is 6 with a remainder of 9.
The number 6 becomes the next digit in our result. 
Result so far: 196.0
Subtract 126 from 135 to get 9.
Include the next digit (0) from the dividend after 9, then repeat: 90 / 21

Step 5:
90 divided by 21 is 4 with a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 1964.0
The remainder is 6 after subtracting 84 from 90.
Grab the next digit (9) from the dividend, add it to 6, then carry on: 69 / 21

Let's proceed to step 6:
When dividing 69 by 21, we get 3 with a remainder of 6.
The next digit of our result is 3. 
Result so far: 19643.0
If we subtract 63 from 69, we get 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:
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: 19643.2
If we subtract 42 from 60, we get 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 8:
180 divided by 21 is 8 with a remainder of 12.
The next digit of our result is 8. 
Result so far: 19643.28
If we subtract 168 from 180, we 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.

Step 9:
21 goes into 120 5 times with a remainder of 15.
The next digit of our result is 5. 
Result so far: 19643.285
Subtract 105 from 120 to get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Going ahead to step 10:
The number 21 fits into 150 7 times, leaving a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 19643.2857
Subtract 147 from 150 to get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 11:
21 can be fit into 30 1 times, resulting in a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 19643.28571
Deduct 21 from 30 and we're left 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.

Let's proceed to step 12:
When dividing 90 by 21, we get 4 with a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 19643.285714
The remainder is 6 after subtracting 84 from 90.
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:
60 divided by 21 is 2 with a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 19643.2857142
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:
If we divide 180 by 21, we get 8 and a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 19643.28571428
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.

Our division results in 19643.28571428 with a remaining 1.2e-08.