Let's divide 133591 by 21
The aim is to understand the frequency of 21 in 133591.

Moving on to step 1:
When dividing 1 by 21, we get 0 with a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
The remainder is 1 after subtracting 0 from 1.
Grab the next digit (3) from the dividend, add it to 1, then carry on: 13 / 21

Step 2:
When dividing 13 by 21, we get 0 with a remainder of 13.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 13, we end up with 13.
Append the next digit (3) from the dividend to 13 and continue with: 133 / 21

On to step 3:
When dividing 133 by 21, we get 6 with a remainder of 7.
The next digit of our result is 6. 
Result so far: 6.0
Deduct 126 from 133 and we're left with 7.
Fetch the next digit (5) from the dividend, attach it to 7 and continue: 75 / 21

On to step 4:
If we divide 75 by 21, we get 3 and a remainder of 12.
The next digit of our result is 3. 
Result so far: 63.0
Subtract 63 from 75 to get 12.
Bring next digit (9) of the dividend behind the 12 and repeat the process: 129 / 21

Step 5:
129 divided by 21 is 6 with a remainder of 3.
The next digit of our result is 6. 
Result so far: 636.0
Subtract 126 from 129 to get 3.
Append the next digit (1) from the dividend to 3 and continue with: 31 / 21

Going ahead to step 6:
21 goes into 31 1 times with a remainder of 10.
Write down 1 as next digit of the result. 
Result so far: 6361.0
Subtract 21 from 31 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.

On to step 7:
When dividing 100 by 21, we get 4 with a remainder of 16.
Put 4 as the next digit of the answer. 
Result so far: 6361.4
Deduct 84 from 100 and we're left 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.

Let's proceed to step 8:
When dividing 160 by 21, we get 7 with a remainder of 13.
Write down 7 as next digit of the result. 
Result so far: 6361.47
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.

Step 9:
21 goes into 130 6 times with a remainder of 4.
The number 6 becomes the next digit in our result. 
Result so far: 6361.476
If we take 126 away from 130, we end up 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 10:
40 divided by 21 is 1 with a remainder of 19.
Use 1 as the next digit of our solution. 
Result so far: 6361.4761
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.

Going ahead to step 11:
21 can be fit into 190 9 times, resulting in a remainder of 1.
The next digit of our result is 9. 
Result so far: 6361.47619
Subtracting 189 from 190 leaves us 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.

On to 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: 6361.47619
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.

Moving on to step 13:
21 goes into 100 4 times with a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 6361.4761904
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.

Moving on to step 14:
21 goes into 160 7 times with a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 6361.47619047
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 outcome is 6361.47619047, with a leftover of 1.3e-08.