415883 divided by 21 
The aim is to understand the frequency of 21 in 415883.

On to step 1:
If we divide 4 by 21, we get 0 and a remainder of 4.
The next digit of our result is 0. 
Result so far: 0.0
If we subtract 0 from 4, we get 4.
Take the next digit (1) from the dividend and append it to 4, then repeat: 41 / 21

Let's proceed to step 2:
When dividing 41 by 21, we get 1 with a remainder of 20.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
Subtracting 21 from 41 leaves us with 20.
Fetch the next digit (5) from the dividend, attach it to 20 and continue: 205 / 21

On to step 3:
21 goes into 205 9 times with a remainder of 16.
The number 9 becomes the next digit in our result. 
Result so far: 19.0
Subtracting 189 from 205 leaves us with 16.
Bring next digit (8) of the dividend behind the 16 and repeat the process: 168 / 21

Let's proceed to step 4:
If we divide 168 by 21, we get 8 and a remainder of 0.
The number 8 becomes the next digit in our result. 
Result so far: 198.0
Subtracting 168 from 168 leaves us with 0.
Take the next digit (8) from the dividend and append it to 0, then repeat: 8 / 21

On to step 5:
If we divide 8 by 21, we get 0 and a remainder of 8.
Write down 0 as next digit of the result. 
Result so far: 1980.0
Deduct 0 from 8 and we're left with 8.
Append the next digit (3) from the dividend to 8 and continue with: 83 / 21

Step 6:
83 divided by 21 is 3 with a remainder of 20.
Write down 3 as next digit of the result. 
Result so far: 19803.0
The remainder is 20 after subtracting 63 from 83.
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 7:
21 goes into 200 9 times with a remainder of 11.
Use 9 as the next digit of our solution. 
Result so far: 19803.9
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.

Advancing to step 8:
110 divided by 21 is 5 with a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 19803.95
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.

Let's proceed to step 9:
50 divided by 21 is 2 with a remainder of 8.
Record the quotient 2 as the next digit in the result. 
Result so far: 19803.952
Deduct 42 from 50 and we're left 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.

Let's proceed to step 10:
21 can be fit into 80 3 times, resulting in a remainder of 17.
The next digit of our result is 3. 
Result so far: 19803.9523
The remainder is 17 after subtracting 63 from 80.
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 11:
21 can be fit into 170 8 times, resulting in a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 19803.95238
The remainder is 2 after subtracting 168 from 170.
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 12:
21 goes into 20 0 times with a remainder of 20.
The next digit of our result is 0. 
Result so far: 19803.95238
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.

Moving on to step 13:
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: 19803.9523809
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.

Step 14:
When dividing 110 by 21, we get 5 with a remainder of 5.
Put 5 as the next digit of the answer. 
Result so far: 19803.95238095
The remainder is 5 after subtracting 105 from 110.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Our division results in 19803.95238095 with a remaining 5e-09.