We look at the division of 368152 by 21 
The aim is to understand the frequency of 21 in 368152.

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
Subtract 0 from 3 to get 3.
Take the next digit (6) from the dividend and append it to 3, then repeat: 36 / 21

Going ahead to step 2:
36 divided by 21 is 1 with a remainder of 15.
Write down 1 as next digit of the result. 
Result so far: 1.0
Deduct 21 from 36 and we're left with 15.
Grab the next digit (8) from the dividend, add it to 15, then carry on: 158 / 21

On to step 3:
21 goes into 158 7 times with a remainder of 11.
Write down 7 as next digit of the result. 
Result so far: 17.0
If we subtract 147 from 158, we get 11.
Include the next digit (1) from the dividend after 11, then repeat: 111 / 21

Advancing to step 4:
If we divide 111 by 21, we get 5 and a remainder of 6.
Use 5 as the next digit of our solution. 
Result so far: 175.0
Subtracting 105 from 111 leaves us with 6.
Grab the next digit (5) from the dividend, add it to 6, then carry on: 65 / 21

On to step 5:
21 goes into 65 3 times with a remainder of 2.
Write down 3 as next digit of the result. 
Result so far: 1753.0
Subtract 63 from 65 to get 2.
Grab the next digit (2) from the dividend, add it to 2, then carry on: 22 / 21

Advancing to step 6:
21 goes into 22 1 times with a remainder of 1.
Put 1 as the next digit of the answer. 
Result so far: 17531.0
If we subtract 21 from 22, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

On to step 7:
21 goes into 10 0 times with a remainder of 10.
The number 0 becomes the next digit in our result. 
Result so far: 17531.0
Deduct 0 from 10 and we're left with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Let's proceed to step 8:
When dividing 100 by 21, we get 4 with a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 17531.04
If we take 84 away from 100, we end up with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Going ahead to step 9:
If we divide 160 by 21, we get 7 and a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 17531.047
Subtract 147 from 160 to get 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Advancing to step 10:
When dividing 130 by 21, we get 6 with a remainder of 4.
Use 6 as the next digit of our solution. 
Result so far: 17531.0476
The remainder is 4 after subtracting 126 from 130.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Going ahead to step 11:
40 divided by 21 is 1 with a remainder of 19.
Write down 1 as next digit of the result. 
Result so far: 17531.04761
If we take 21 away from 40, we end up with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Moving on to step 12:
190 divided by 21 is 9 with a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 17531.047619
If we subtract 189 from 190, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Moving on to step 13:
If we divide 10 by 21, we get 0 and a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 17531.047619
If we take 0 away from 10, we end up with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Advancing to step 14:
The number 21 fits into 100 4 times, leaving a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 17531.04761904
If we take 84 away from 100, we end up with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

After the division, we end up with 17531.04761904 and a remainder of 1.6e-08.