843754 divided by 21 
The aim is to understand the frequency of 21 in 843754.

Step 1:
21 goes into 8 0 times with a remainder of 8.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtract 0 from 8 to get 8.
Append the next digit (4) from the dividend to 8 and continue with: 84 / 21

On to step 2:
If we divide 84 by 21, we get 4 and a remainder of 0.
Record the quotient 4 as the next digit in the result. 
Result so far: 4.0
If we subtract 84 from 84, we get 0.
Grab the next digit (3) from the dividend, add it to 0, then carry on: 3 / 21

Let's proceed to step 3:
If we divide 3 by 21, we get 0 and a remainder of 3.
The next digit of our result is 0. 
Result so far: 40.0
The remainder is 3 after subtracting 0 from 3.
Grab the next digit (7) from the dividend, add it to 3, then carry on: 37 / 21

Advancing to step 4:
If we divide 37 by 21, we get 1 and a remainder of 16.
Put 1 as the next digit of the answer. 
Result so far: 401.0
The remainder is 16 after subtracting 21 from 37.
Bring next digit (5) of the dividend behind the 16 and repeat the process: 165 / 21

Step 5:
If we divide 165 by 21, we get 7 and a remainder of 18.
Put 7 as the next digit of the answer. 
Result so far: 4017.0
Subtracting 147 from 165 leaves us with 18.
Take the next digit (4) from the dividend and append it to 18, then repeat: 184 / 21

Step 6:
184 divided by 21 is 8 with a remainder of 16.
Put 8 as the next digit of the answer. 
Result so far: 40178.0
Subtract 168 from 184 to get 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Advancing to step 7:
160 divided by 21 is 7 with a remainder of 13.
Write down 7 as next digit of the result. 
Result so far: 40178.7
If we take 147 away from 160, we end up with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

On to step 8:
The number 21 fits into 130 6 times, leaving a remainder of 4.
The next digit of our result is 6. 
Result so far: 40178.76
Deduct 126 from 130 and we're left 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 9:
When dividing 40 by 21, we get 1 with a remainder of 19.
Put 1 as the next digit of the answer. 
Result so far: 40178.761
Subtract 21 from 40 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Advancing to step 10:
190 divided by 21 is 9 with a remainder of 1.
Put 9 as the next digit of the answer. 
Result so far: 40178.7619
Deduct 189 from 190 and we're left with 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 11:
10 divided by 21 is 0 with a remainder of 10.
The next digit of our result is 0. 
Result so far: 40178.7619
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.

Let's proceed to step 12:
If we divide 100 by 21, we get 4 and a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 40178.761904
The remainder is 16 after subtracting 84 from 100.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Advancing to step 13:
If we divide 160 by 21, we get 7 and a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 40178.7619047
Subtracting 147 from 160 leaves us with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Moving on to step 14:
21 can be fit into 130 6 times, resulting in a remainder of 4.
Write down 6 as next digit of the result. 
Result so far: 40178.76190476
The remainder is 4 after subtracting 126 from 130.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

The final outcome is 40178.76190476, with a leftover of 4e-09.