We divide 381015 by 21
The aim is to understand the frequency of 21 in 381015.

Advancing to step 1:
If we divide 3 by 21, we get 0 and a remainder of 3.
Use 0 as the next digit of our solution. 
Result so far: 0.0
The remainder is 3 after subtracting 0 from 3.
Fetch the next digit (8) from the dividend, attach it to 3 and continue: 38 / 21

Let's proceed to step 2:
38 divided by 21 is 1 with a remainder of 17.
Use 1 as the next digit of our solution. 
Result so far: 1.0
The remainder is 17 after subtracting 21 from 38.
Include the next digit (1) from the dividend after 17, then repeat: 171 / 21

On to step 3:
The number 21 fits into 171 8 times, leaving a remainder of 3.
The next digit of our result is 8. 
Result so far: 18.0
Deduct 168 from 171 and we're left with 3.
Include the next digit (0) from the dividend after 3, then repeat: 30 / 21

Let's proceed to step 4:
If we divide 30 by 21, we get 1 and a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 181.0
The remainder is 9 after subtracting 21 from 30.
Include the next digit (1) from the dividend after 9, then repeat: 91 / 21

Going ahead to step 5:
21 goes into 91 4 times with a remainder of 7.
Put 4 as the next digit of the answer. 
Result so far: 1814.0
If we subtract 84 from 91, we get 7.
Include the next digit (5) from the dividend after 7, then repeat: 75 / 21

Moving on to step 6:
75 divided by 21 is 3 with a remainder of 12.
The next digit of our result is 3. 
Result so far: 18143.0
Subtract 63 from 75 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.

Advancing to step 7:
21 can be fit into 120 5 times, resulting in a remainder of 15.
Write down 5 as next digit of the result. 
Result so far: 18143.5
Deduct 105 from 120 and we're left 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.

Let's proceed to step 8:
21 can be fit into 150 7 times, resulting in a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 18143.57
If we take 147 away from 150, we end up with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

On to step 9:
30 divided by 21 is 1 with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 18143.571
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.

On to step 10:
90 divided by 21 is 4 with a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 18143.5714
Subtract 84 from 90 to 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.

Advancing to step 11:
The number 21 fits into 60 2 times, leaving a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 18143.57142
Subtracting 42 from 60 leaves us 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 12:
180 divided by 21 is 8 with a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 18143.571428
The remainder is 12 after subtracting 168 from 180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Advancing to step 13:
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: 18143.5714285
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.

Advancing to step 14:
21 can be fit into 150 7 times, resulting in a remainder of 3.
The next digit of our result is 7. 
Result so far: 18143.57142857
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.

The final outcome is 18143.57142857, with a leftover of 3e-09.