We look at the division of 874933 by 21 
The aim is to understand the frequency of 21 in 874933.

Let's proceed to step 1:
The number 21 fits into 8 0 times, leaving a remainder of 8.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 8 and we're left with 8.
Grab the next digit (7) from the dividend, add it to 8, then carry on: 87 / 21

Step 2:
87 divided by 21 is 4 with a remainder of 3.
Record the quotient 4 as the next digit in the result. 
Result so far: 4.0
The remainder is 3 after subtracting 84 from 87.
Include the next digit (4) from the dividend after 3, then repeat: 34 / 21

Advancing to step 3:
If we divide 34 by 21, we get 1 and a remainder of 13.
Put 1 as the next digit of the answer. 
Result so far: 41.0
If we subtract 21 from 34, we get 13.
Take the next digit (9) from the dividend and append it to 13, then repeat: 139 / 21

On to step 4:
If we divide 139 by 21, we get 6 and a remainder of 13.
Put 6 as the next digit of the answer. 
Result so far: 416.0
If we take 126 away from 139, we end up with 13.
Fetch the next digit (3) from the dividend, attach it to 13 and continue: 133 / 21

Let's proceed to step 5:
The number 21 fits into 133 6 times, leaving a remainder of 7.
Put 6 as the next digit of the answer. 
Result so far: 4166.0
If we take 126 away from 133, we end up with 7.
Include the next digit (3) from the dividend after 7, then repeat: 73 / 21

Let's proceed to step 6:
When dividing 73 by 21, we get 3 with a remainder of 10.
The next digit of our result is 3. 
Result so far: 41663.0
If we subtract 63 from 73, we get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Going ahead to step 7:
If we divide 100 by 21, we get 4 and a remainder of 16.
Write down 4 as next digit of the result. 
Result so far: 41663.4
Subtracting 84 from 100 leaves us 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.

Advancing to step 8:
21 goes into 160 7 times with a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 41663.47
If we subtract 147 from 160, we 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.

Let's proceed to step 9:
The number 21 fits into 130 6 times, leaving a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 41663.476
Subtract 126 from 130 to get 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Step 10:
When dividing 40 by 21, we get 1 with a remainder of 19.
Write down 1 as next digit of the result. 
Result so far: 41663.4761
Subtract 21 from 40 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Going ahead to step 11:
If we divide 190 by 21, we get 9 and a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 41663.47619
If we take 189 away from 190, we end up with 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 12:
21 can be fit into 10 0 times, resulting in a remainder of 10.
Write down 0 as next digit of the result. 
Result so far: 41663.47619
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 13:
When dividing 100 by 21, we get 4 with a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 41663.4761904
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.

Advancing to step 14:
160 divided by 21 is 7 with a remainder of 13.
The next digit of our result is 7. 
Result so far: 41663.47619047
If we subtract 147 from 160, we 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.

The final result is 41663.47619047 with a remainder of 1.3e-08.