We're dividing 918378 by 21 
The aim is to understand the frequency of 21 in 918378.

Moving on to step 1:
21 can be fit into 9 0 times, resulting in a remainder of 9.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we subtract 0 from 9, we get 9.
Append the next digit (1) from the dividend to 9 and continue with: 91 / 21

Advancing to step 2:
If we divide 91 by 21, we get 4 and a remainder of 7.
Write down 4 as next digit of the result. 
Result so far: 4.0
Subtracting 84 from 91 leaves us with 7.
Append the next digit (8) from the dividend to 7 and continue with: 78 / 21

Step 3:
The number 21 fits into 78 3 times, leaving a remainder of 15.
Record the quotient 3 as the next digit in the result. 
Result so far: 43.0
The remainder is 15 after subtracting 63 from 78.
Bring next digit (3) of the dividend behind the 15 and repeat the process: 153 / 21

Step 4:
153 divided by 21 is 7 with a remainder of 6.
The next digit of our result is 7. 
Result so far: 437.0
Deduct 147 from 153 and we're left with 6.
Bring next digit (7) of the dividend behind the 6 and repeat the process: 67 / 21

Advancing to step 5:
The number 21 fits into 67 3 times, leaving a remainder of 4.
The number 3 becomes the next digit in our result. 
Result so far: 4373.0
If we subtract 63 from 67, we get 4.
Take the next digit (8) from the dividend and append it to 4, then repeat: 48 / 21

Moving on to step 6:
48 divided by 21 is 2 with a remainder of 6.
The number 2 becomes the next digit in our result. 
Result so far: 43732.0
If we subtract 42 from 48, 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.

On to step 7:
The number 21 fits into 60 2 times, leaving a remainder of 18.
Write down 2 as next digit of the result. 
Result so far: 43732.2
If we take 42 away from 60, we end up 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.

Advancing to step 8:
21 can be fit into 180 8 times, resulting in a remainder of 12.
The next digit of our result is 8. 
Result so far: 43732.28
If we take 168 away from 180, we end up 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.

Moving on to step 9:
21 can be fit into 120 5 times, resulting in a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 43732.285
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.

Moving on to step 10:
If we divide 150 by 21, we get 7 and a remainder of 3.
The number 7 becomes the next digit in our result. 
Result so far: 43732.2857
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.

Moving on to step 11:
When dividing 30 by 21, we get 1 with a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 43732.28571
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.

Advancing to step 12:
When dividing 90 by 21, we get 4 with a remainder of 6.
Write down 4 as next digit of the result. 
Result so far: 43732.285714
If we subtract 84 from 90, 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.

Moving on to step 13:
60 divided by 21 is 2 with a remainder of 18.
Write down 2 as next digit of the result. 
Result so far: 43732.2857142
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.

Moving on to step 14:
180 divided by 21 is 8 with a remainder of 12.
Write down 8 as next digit of the result. 
Result so far: 43732.28571428
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.

The final outcome is 43732.28571428, with a leftover of 1.2e-08.