339933 divided by 21 
The aim is to understand the frequency of 21 in 339933.

Advancing to step 1:
21 can be fit into 3 0 times, resulting in a remainder of 3.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we take 0 away from 3, we end up with 3.
Take the next digit (3) from the dividend and append it to 3, then repeat: 33 / 21

On to step 2:
If we divide 33 by 21, we get 1 and a remainder of 12.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
Deduct 21 from 33 and we're left with 12.
Bring next digit (9) of the dividend behind the 12 and repeat the process: 129 / 21

Moving on to step 3:
If we divide 129 by 21, we get 6 and a remainder of 3.
Put 6 as the next digit of the answer. 
Result so far: 16.0
Subtract 126 from 129 to get 3.
Include the next digit (9) from the dividend after 3, then repeat: 39 / 21

Moving on to step 4:
If we divide 39 by 21, we get 1 and a remainder of 18.
The next digit of our result is 1. 
Result so far: 161.0
Subtracting 21 from 39 leaves us with 18.
Include the next digit (3) from the dividend after 18, then repeat: 183 / 21

On to step 5:
If we divide 183 by 21, we get 8 and a remainder of 15.
Use 8 as the next digit of our solution. 
Result so far: 1618.0
Deduct 168 from 183 and we're left with 15.
Bring next digit (3) of the dividend behind the 15 and repeat the process: 153 / 21

Going ahead to step 6:
The number 21 fits into 153 7 times, leaving a remainder of 6.
The number 7 becomes the next digit in our result. 
Result so far: 16187.0
Deduct 147 from 153 and we're left with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Moving on to step 7:
21 can be fit into 60 2 times, resulting in a remainder of 18.
Use 2 as the next digit of our solution. 
Result so far: 16187.2
The remainder is 18 after subtracting 42 from 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Going ahead to step 8:
When dividing 180 by 21, we get 8 with a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 16187.28
The remainder is 12 after subtracting 168 from 180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Let's proceed to step 9:
If we divide 120 by 21, we get 5 and a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 16187.285
If we subtract 105 from 120, 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.

Moving on to step 10:
21 goes into 150 7 times with a remainder of 3.
Use 7 as the next digit of our solution. 
Result so far: 16187.2857
The remainder is 3 after subtracting 147 from 150.
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 11:
When dividing 30 by 21, we get 1 with a remainder of 9.
Record the quotient 1 as the next digit in the result. 
Result so far: 16187.28571
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.

Let's proceed to step 12:
When dividing 90 by 21, we get 4 with a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 16187.285714
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.

Let's proceed to step 13:
If we divide 60 by 21, we get 2 and a remainder of 18.
Use 2 as the next digit of our solution. 
Result so far: 16187.2857142
Subtract 42 from 60 to get 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Let's proceed to step 14:
21 can be fit into 180 8 times, resulting in a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 16187.28571428
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.

After the division, we end up with 16187.28571428 and a remainder of 1.2e-08.