993513 ÷ 21 
The aim is to understand the frequency of 21 in 993513.

Step 1:
9 divided by 21 is 0 with a remainder of 9.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 9, we end up with 9.
Append the next digit (9) from the dividend to 9 and continue with: 99 / 21

Step 2:
The number 21 fits into 99 4 times, leaving a remainder of 15.
Write down 4 as next digit of the result. 
Result so far: 4.0
If we take 84 away from 99, we end up with 15.
Bring next digit (3) of the dividend behind the 15 and repeat the process: 153 / 21

Advancing to step 3:
21 goes into 153 7 times with a remainder of 6.
Use 7 as the next digit of our solution. 
Result so far: 47.0
The remainder is 6 after subtracting 147 from 153.
Fetch the next digit (5) from the dividend, attach it to 6 and continue: 65 / 21

Let's proceed to step 4:
When dividing 65 by 21, we get 3 with a remainder of 2.
The next digit of our result is 3. 
Result so far: 473.0
Deduct 63 from 65 and we're left with 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 21

Going ahead to step 5:
21 goes into 21 1 times with a remainder of 0.
Write down 1 as next digit of the result. 
Result so far: 4731.0
If we subtract 21 from 21, we get 0.
Append the next digit (3) from the dividend to 0 and continue with: 3 / 21

Advancing to step 6:
If we divide 3 by 21, we get 0 and a remainder of 3.
Write down 0 as next digit of the result. 
Result so far: 47310.0
Deduct 0 from 3 and we're left with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 7:
When dividing 30 by 21, we get 1 with a remainder of 9.
Put 1 as the next digit of the answer. 
Result so far: 47310.1
Deduct 21 from 30 and we're left 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.

Let's proceed to step 8:
90 divided by 21 is 4 with a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 47310.14
The remainder is 6 after subtracting 84 from 90.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

On to step 9:
21 can be fit into 60 2 times, resulting in a remainder of 18.
The number 2 becomes the next digit in our result. 
Result so far: 47310.142
Deduct 42 from 60 and we're left 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.

Moving on to step 10:
180 divided by 21 is 8 with a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 47310.1428
Deduct 168 from 180 and we're left with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Going ahead to step 11:
21 can be fit into 120 5 times, resulting in a remainder of 15.
The next digit of our result is 5. 
Result so far: 47310.14285
Deduct 105 from 120 and we're left 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.

Going ahead to step 12:
If we divide 150 by 21, we get 7 and a remainder of 3.
The number 7 becomes the next digit in our result. 
Result so far: 47310.142857
Deduct 147 from 150 and we're left with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

On to step 13:
When dividing 30 by 21, we get 1 with a remainder of 9.
The next digit of our result is 1. 
Result so far: 47310.1428571
Deduct 21 from 30 and we're left 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.

Advancing to step 14:
If we divide 90 by 21, we get 4 and a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 47310.14285714
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.

After the division, we end up with 47310.14285714 and a remainder of 6e-09.