321424 ÷ 21 
The aim is to understand the frequency of 21 in 321424.

Advancing to step 1:
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: 0.0
If we take 0 away from 3, we end up with 3.
Take the next digit (2) from the dividend and append it to 3, then repeat: 32 / 21

Let's proceed to step 2:
32 divided by 21 is 1 with a remainder of 11.
Put 1 as the next digit of the answer. 
Result so far: 1.0
If we subtract 21 from 32, we get 11.
Bring next digit (1) of the dividend behind the 11 and repeat the process: 111 / 21

On to step 3:
When dividing 111 by 21, we get 5 with a remainder of 6.
Use 5 as the next digit of our solution. 
Result so far: 15.0
Subtracting 105 from 111 leaves us with 6.
Include the next digit (4) from the dividend after 6, then repeat: 64 / 21

Moving on to step 4:
When dividing 64 by 21, we get 3 with a remainder of 1.
Record the quotient 3 as the next digit in the result. 
Result so far: 153.0
Subtracting 63 from 64 leaves us with 1.
Include the next digit (2) from the dividend after 1, then repeat: 12 / 21

Going ahead to step 5:
21 can be fit into 12 0 times, resulting in a remainder of 12.
Record the quotient 0 as the next digit in the result. 
Result so far: 1530.0
If we take 0 away from 12, we end up with 12.
Grab the next digit (4) from the dividend, add it to 12, then carry on: 124 / 21

Let's proceed to step 6:
If we divide 124 by 21, we get 5 and a remainder of 19.
The number 5 becomes the next digit in our result. 
Result so far: 15305.0
Deduct 105 from 124 and we're left with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Step 7:
21 goes into 190 9 times with a remainder of 1.
Use 9 as the next digit of our solution. 
Result so far: 15305.9
Subtract 189 from 190 to 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.

Advancing to step 8:
The number 21 fits into 10 0 times, leaving a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 15305.9
Subtracting 0 from 10 leaves us 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.

Step 9:
21 goes into 100 4 times with a remainder of 16.
The next digit of our result is 4. 
Result so far: 15305.904
Subtracting 84 from 100 leaves us 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 10:
When dividing 160 by 21, we get 7 with a remainder of 13.
The number 7 becomes the next digit in our result. 
Result so far: 15305.9047
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.

Going ahead to step 11:
130 divided by 21 is 6 with a remainder of 4.
The number 6 becomes the next digit in our result. 
Result so far: 15305.90476
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.

Step 12:
When dividing 40 by 21, we get 1 with a remainder of 19.
Write down 1 as next digit of the result. 
Result so far: 15305.904761
If we take 21 away from 40, we end up with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Step 13:
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: 15305.9047619
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.

On to step 14:
10 divided by 21 is 0 with a remainder of 10.
The number 0 becomes the next digit in our result. 
Result so far: 15305.9047619
Subtracting 0 from 10 leaves us 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.

The final outcome is 15305.9047619, with a leftover of 1e-08.