859489 ÷ 21 
The aim is to understand the frequency of 21 in 859489.

On to step 1:
When dividing 8 by 21, we get 0 with a remainder of 8.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 8 and we're left with 8.
Bring next digit (5) of the dividend behind the 8 and repeat the process: 85 / 21

Advancing to step 2:
If we divide 85 by 21, we get 4 and a remainder of 1.
Record the quotient 4 as the next digit in the result. 
Result so far: 4.0
The remainder is 1 after subtracting 84 from 85.
Fetch the next digit (9) from the dividend, attach it to 1 and continue: 19 / 21

Going ahead to step 3:
If we divide 19 by 21, we get 0 and a remainder of 19.
The next digit of our result is 0. 
Result so far: 40.0
Deduct 0 from 19 and we're left with 19.
Append the next digit (4) from the dividend to 19 and continue with: 194 / 21

Let's proceed to step 4:
When dividing 194 by 21, we get 9 with a remainder of 5.
The number 9 becomes the next digit in our result. 
Result so far: 409.0
Subtract 189 from 194 to get 5.
Include the next digit (8) from the dividend after 5, then repeat: 58 / 21

Advancing to step 5:
When dividing 58 by 21, we get 2 with a remainder of 16.
Put 2 as the next digit of the answer. 
Result so far: 4092.0
If we take 42 away from 58, we end up with 16.
Append the next digit (9) from the dividend to 16 and continue with: 169 / 21

Going ahead to step 6:
21 can be fit into 169 8 times, resulting in a remainder of 1.
Put 8 as the next digit of the answer. 
Result so far: 40928.0
If we subtract 168 from 169, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Moving on to step 7:
21 goes into 10 0 times with a remainder of 10.
The next digit of our result is 0. 
Result so far: 40928.0
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.

Step 8:
21 can be fit into 100 4 times, resulting in a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 40928.04
Deduct 84 from 100 and we're left with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

On to step 9:
The number 21 fits into 160 7 times, leaving a remainder of 13.
Use 7 as the next digit of our solution. 
Result so far: 40928.047
The remainder is 13 after subtracting 147 from 160.
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 10:
The number 21 fits into 130 6 times, leaving a remainder of 4.
Use 6 as the next digit of our solution. 
Result so far: 40928.0476
Subtracting 126 from 130 leaves us 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.

On to step 11:
21 can be fit into 40 1 times, resulting in a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 40928.04761
If we subtract 21 from 40, we 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.

Step 12:
21 can be fit into 190 9 times, resulting in a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 40928.047619
Subtracting 189 from 190 leaves us 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.

Moving on to step 13:
10 divided by 21 is 0 with a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 40928.047619
If we subtract 0 from 10, we get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 14:
21 goes into 100 4 times with a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 40928.04761904
If we subtract 84 from 100, we 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.

After the division, we end up with 40928.04761904 and a remainder of 1.6e-08.