We're dividing 916093 by 21 
The aim is to understand the frequency of 21 in 916093.

On to step 1:
If we divide 9 by 21, we get 0 and 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.
Grab the next digit (1) from the dividend, add it to 9, then carry on: 91 / 21

Going ahead to step 2:
21 goes into 91 4 times with a remainder of 7.
Put 4 as the next digit of the answer. 
Result so far: 4.0
If we take 84 away from 91, we end up with 7.
Grab the next digit (6) from the dividend, add it to 7, then carry on: 76 / 21

Let's proceed to step 3:
76 divided by 21 is 3 with a remainder of 13.
Use 3 as the next digit of our solution. 
Result so far: 43.0
If we take 63 away from 76, we end up with 13.
Take the next digit (0) from the dividend and append it to 13, then repeat: 130 / 21

Moving on to step 4:
When dividing 130 by 21, we get 6 with a remainder of 4.
The number 6 becomes the next digit in our result. 
Result so far: 436.0
If we subtract 126 from 130, we get 4.
Take the next digit (9) from the dividend and append it to 4, then repeat: 49 / 21

Step 5:
If we divide 49 by 21, we get 2 and a remainder of 7.
Write down 2 as next digit of the result. 
Result so far: 4362.0
Deduct 42 from 49 and we're left with 7.
Grab the next digit (3) from the dividend, add it to 7, then carry on: 73 / 21

Moving on to step 6:
If we divide 73 by 21, we get 3 and a remainder of 10.
The number 3 becomes the next digit in our result. 
Result so far: 43623.0
If we take 63 away from 73, 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.

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: 43623.4
The remainder is 16 after subtracting 84 from 100.
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:
If we divide 160 by 21, we get 7 and a remainder of 13.
Use 7 as the next digit of our solution. 
Result so far: 43623.47
Deduct 147 from 160 and we're left with 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:
130 divided by 21 is 6 with a remainder of 4.
Use 6 as the next digit of our solution. 
Result so far: 43623.476
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.

On to step 10:
The number 21 fits into 40 1 times, leaving a remainder of 19.
Write down 1 as next digit of the result. 
Result so far: 43623.4761
If we subtract 21 from 40, we 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.

Moving on to step 11:
21 can be fit into 190 9 times, resulting in a remainder of 1.
Write down 9 as next digit of the result. 
Result so far: 43623.47619
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.

Step 12:
The number 21 fits into 10 0 times, leaving a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 43623.47619
Subtract 0 from 10 to 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.

Advancing to step 13:
21 goes into 100 4 times with a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 43623.4761904
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.

Moving on to step 14:
The number 21 fits into 160 7 times, leaving a remainder of 13.
The next digit of our result is 7. 
Result so far: 43623.47619047
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.

The final outcome is 43623.47619047, with a leftover of 1.3e-08.