213648 divided by 21 
The aim is to understand the frequency of 21 in 213648.

Advancing to step 1:
21 goes into 2 0 times with a remainder of 2.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtracting 0 from 2 leaves us with 2.
Include the next digit (1) from the dividend after 2, then repeat: 21 / 21

Let's proceed to step 2:
21 divided by 21 is 1 with a remainder of 0.
Put 1 as the next digit of the answer. 
Result so far: 1.0
Subtracting 21 from 21 leaves us with 0.
Fetch the next digit (3) from the dividend, attach it to 0 and continue: 3 / 21

Moving on to step 3:
When dividing 3 by 21, we get 0 with a remainder of 3.
Put 0 as the next digit of the answer. 
Result so far: 10.0
Deduct 0 from 3 and we're left with 3.
Include the next digit (6) from the dividend after 3, then repeat: 36 / 21

Step 4:
21 can be fit into 36 1 times, resulting in a remainder of 15.
The next digit of our result is 1. 
Result so far: 101.0
Deduct 21 from 36 and we're left with 15.
Fetch the next digit (4) from the dividend, attach it to 15 and continue: 154 / 21

Going ahead to step 5:
If we divide 154 by 21, we get 7 and a remainder of 7.
The next digit of our result is 7. 
Result so far: 1017.0
Subtract 147 from 154 to get 7.
Include the next digit (8) from the dividend after 7, then repeat: 78 / 21

On to step 6:
The number 21 fits into 78 3 times, leaving a remainder of 15.
Use 3 as the next digit of our solution. 
Result so far: 10173.0
If we subtract 63 from 78, we 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.

Advancing to step 7:
The number 21 fits into 150 7 times, leaving a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 10173.7
Subtract 147 from 150 to get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Going ahead to step 8:
21 can be fit into 30 1 times, resulting in a remainder of 9.
Put 1 as the next digit of the answer. 
Result so far: 10173.71
If we take 21 away from 30, we end up with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Step 9:
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: 10173.714
Subtract 84 from 90 to 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.

Going ahead to step 10:
21 goes into 60 2 times with a remainder of 18.
Use 2 as the next digit of our solution. 
Result so far: 10173.7142
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.

On to step 11:
If we divide 180 by 21, we get 8 and a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 10173.71428
Subtract 168 from 180 to get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

On to step 12:
The number 21 fits into 120 5 times, leaving a remainder of 15.
Record the quotient 5 as the next digit in the result. 
Result so far: 10173.714285
If we take 105 away from 120, we end up with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Step 13:
If we divide 150 by 21, we get 7 and a remainder of 3.
Record the quotient 7 as the next digit in the result. 
Result so far: 10173.7142857
Subtract 147 from 150 to get 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Advancing to step 14:
The number 21 fits into 30 1 times, leaving a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 10173.71428571
Subtract 21 from 30 to 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.

Our division results in 10173.71428571 with a remaining 9e-09.