891938 divided by 21 
The aim is to understand the frequency of 21 in 891938.

Step 1:
If we divide 8 by 21, we get 0 and a remainder of 8.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
The remainder is 8 after subtracting 0 from 8.
Fetch the next digit (9) from the dividend, attach it to 8 and continue: 89 / 21

On to step 2:
The number 21 fits into 89 4 times, leaving a remainder of 5.
The next digit of our result is 4. 
Result so far: 4.0
Subtracting 84 from 89 leaves us with 5.
Take the next digit (1) from the dividend and append it to 5, then repeat: 51 / 21

Let's proceed to step 3:
When dividing 51 by 21, we get 2 with a remainder of 9.
The next digit of our result is 2. 
Result so far: 42.0
If we take 42 away from 51, we end up with 9.
Bring next digit (9) of the dividend behind the 9 and repeat the process: 99 / 21

On to step 4:
The number 21 fits into 99 4 times, leaving a remainder of 15.
Record the quotient 4 as the next digit in the result. 
Result so far: 424.0
Subtract 84 from 99 to get 15.
Append the next digit (3) from the dividend to 15 and continue with: 153 / 21

On to step 5:
If we divide 153 by 21, we get 7 and a remainder of 6.
Record the quotient 7 as the next digit in the result. 
Result so far: 4247.0
Subtract 147 from 153 to get 6.
Append the next digit (8) from the dividend to 6 and continue with: 68 / 21

Going ahead to step 6:
21 goes into 68 3 times with a remainder of 5.
Write down 3 as next digit of the result. 
Result so far: 42473.0
Deduct 63 from 68 and we're left 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.

Going ahead to step 7:
21 can be fit into 50 2 times, resulting in a remainder of 8.
Write down 2 as next digit of the result. 
Result so far: 42473.2
Subtracting 42 from 50 leaves us with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Let's proceed to step 8:
80 divided by 21 is 3 with a remainder of 17.
Write down 3 as next digit of the result. 
Result so far: 42473.23
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.

Let's proceed to step 9:
When dividing 170 by 21, we get 8 with a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 42473.238
Subtract 168 from 170 to get 2.
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:
The number 21 fits into 20 0 times, leaving a remainder of 20.
The next digit of our result is 0. 
Result so far: 42473.238
If we take 0 away from 20, we end up with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Moving on to step 11:
When dividing 200 by 21, we get 9 with a remainder of 11.
The number 9 becomes the next digit in our result. 
Result so far: 42473.23809
Subtract 189 from 200 to get 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Moving on to step 12:
When dividing 110 by 21, we get 5 with a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 42473.238095
Subtract 105 from 110 to get 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 13:
When dividing 50 by 21, we get 2 with a remainder of 8.
Put 2 as the next digit of the answer. 
Result so far: 42473.2380952
Subtract 42 from 50 to 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.

Let's proceed to step 14:
If we divide 80 by 21, we get 3 and a remainder of 17.
Write down 3 as next digit of the result. 
Result so far: 42473.23809523
Subtracting 63 from 80 leaves us with 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 final result is 42473.23809523 with a remainder of 1.7e-08.