We look at the division of 956566 by 21 
The aim is to understand the frequency of 21 in 956566.

Let's proceed to step 1:
The number 21 fits into 9 0 times, leaving a remainder of 9.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 9 to get 9.
Include the next digit (5) from the dividend after 9, then repeat: 95 / 21

On to step 2:
When dividing 95 by 21, we get 4 with a remainder of 11.
Write down 4 as next digit of the result. 
Result so far: 4.0
If we take 84 away from 95, we end up with 11.
Bring next digit (6) of the dividend behind the 11 and repeat the process: 116 / 21

Let's proceed to step 3:
When dividing 116 by 21, we get 5 with a remainder of 11.
Put 5 as the next digit of the answer. 
Result so far: 45.0
The remainder is 11 after subtracting 105 from 116.
Grab the next digit (5) from the dividend, add it to 11, then carry on: 115 / 21

On to step 4:
21 can be fit into 115 5 times, resulting in a remainder of 10.
Use 5 as the next digit of our solution. 
Result so far: 455.0
Subtract 105 from 115 to get 10.
Append the next digit (6) from the dividend to 10 and continue with: 106 / 21

Let's proceed to step 5:
106 divided by 21 is 5 with a remainder of 1.
Write down 5 as next digit of the result. 
Result so far: 4555.0
Subtracting 105 from 106 leaves us with 1.
Bring next digit (6) of the dividend behind the 1 and repeat the process: 16 / 21

On to step 6:
16 divided by 21 is 0 with a remainder of 16.
Put 0 as the next digit of the answer. 
Result so far: 45550.0
If we subtract 0 from 16, we get 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 7:
21 can be fit into 160 7 times, resulting in a remainder of 13.
The number 7 becomes the next digit in our result. 
Result so far: 45550.7
If we take 147 away from 160, we end up 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.

Going ahead to step 8:
21 can be fit into 130 6 times, resulting in a remainder of 4.
The next digit of our result is 6. 
Result so far: 45550.76
Subtracting 126 from 130 leaves us with 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 9:
The number 21 fits into 40 1 times, leaving a remainder of 19.
Put 1 as the next digit of the answer. 
Result so far: 45550.761
The remainder is 19 after subtracting 21 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Advancing to step 10:
The number 21 fits into 190 9 times, leaving a remainder of 1.
Use 9 as the next digit of our solution. 
Result so far: 45550.7619
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.

Let's proceed to step 11:
When dividing 10 by 21, we get 0 with a remainder of 10.
The number 0 becomes the next digit in our result. 
Result so far: 45550.7619
If we subtract 0 from 10, 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.

On to step 12:
If we divide 100 by 21, we get 4 and a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 45550.761904
Subtract 84 from 100 to get 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 13:
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: 45550.7619047
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.

Going ahead to step 14:
The number 21 fits into 130 6 times, leaving a remainder of 4.
The next digit of our result is 6. 
Result so far: 45550.76190476
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.

Our division results in 45550.76190476 with a remaining 4e-09.