434243 divided by 21 
The aim is to understand the frequency of 21 in 434243.

On to step 1:
21 goes into 4 0 times with a remainder of 4.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we subtract 0 from 4, we get 4.
Fetch the next digit (3) from the dividend, attach it to 4 and continue: 43 / 21

Moving on to step 2:
If we divide 43 by 21, we get 2 and a remainder of 1.
Write down 2 as next digit of the result. 
Result so far: 2.0
Subtract 42 from 43 to get 1.
Grab the next digit (4) from the dividend, add it to 1, then carry on: 14 / 21

Advancing to step 3:
The number 21 fits into 14 0 times, leaving a remainder of 14.
Put 0 as the next digit of the answer. 
Result so far: 20.0
The remainder is 14 after subtracting 0 from 14.
Include the next digit (2) from the dividend after 14, then repeat: 142 / 21

Step 4:
142 divided by 21 is 6 with a remainder of 16.
Write down 6 as next digit of the result. 
Result so far: 206.0
Subtract 126 from 142 to get 16.
Take the next digit (4) from the dividend and append it to 16, then repeat: 164 / 21

On to step 5:
When dividing 164 by 21, we get 7 with a remainder of 17.
Use 7 as the next digit of our solution. 
Result so far: 2067.0
If we take 147 away from 164, we end up with 17.
Grab the next digit (3) from the dividend, add it to 17, then carry on: 173 / 21

Moving on to step 6:
173 divided by 21 is 8 with a remainder of 5.
Put 8 as the next digit of the answer. 
Result so far: 20678.0
If we take 168 away from 173, we end up with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Let's proceed to step 7:
If we divide 50 by 21, we get 2 and a remainder of 8.
The next digit of our result is 2. 
Result so far: 20678.2
If we subtract 42 from 50, we get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Step 8:
If we divide 80 by 21, we get 3 and a remainder of 17.
The next digit of our result is 3. 
Result so far: 20678.23
The remainder is 17 after subtracting 63 from 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Moving on to step 9:
If we divide 170 by 21, we get 8 and a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 20678.238
The remainder is 2 after subtracting 168 from 170.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

On to step 10:
If we divide 20 by 21, we get 0 and a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 20678.238
The remainder is 20 after subtracting 0 from 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Advancing to step 11:
200 divided by 21 is 9 with a remainder of 11.
Put 9 as the next digit of the answer. 
Result so far: 20678.23809
Subtracting 189 from 200 leaves us with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Step 12:
When dividing 110 by 21, we get 5 with a remainder of 5.
The next digit of our result is 5. 
Result so far: 20678.238095
If we take 105 away from 110, we end up with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Advancing to step 13:
When dividing 50 by 21, we get 2 with a remainder of 8.
Write down 2 as next digit of the result. 
Result so far: 20678.2380952
If we subtract 42 from 50, we get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Advancing to step 14:
When dividing 80 by 21, we get 3 with a remainder of 17.
Write down 3 as next digit of the result. 
Result so far: 20678.23809523
Subtract 63 from 80 to get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

The quotient of the division is 20678.23809523, and the remainder is 1.7e-08.