We look at the division of 285969 by 21 
The aim is to understand the frequency of 21 in 285969.

Let's proceed to step 1:
21 can be fit into 2 0 times, resulting in a remainder of 2.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 2, we get 2.
Include the next digit (8) from the dividend after 2, then repeat: 28 / 21

Moving on to step 2:
When dividing 28 by 21, we get 1 with a remainder of 7.
Write down 1 as next digit of the result. 
Result so far: 1.0
If we take 21 away from 28, we end up with 7.
Grab the next digit (5) from the dividend, add it to 7, then carry on: 75 / 21

Advancing to step 3:
21 goes into 75 3 times with a remainder of 12.
The number 3 becomes the next digit in our result. 
Result so far: 13.0
The remainder is 12 after subtracting 63 from 75.
Fetch the next digit (9) from the dividend, attach it to 12 and continue: 129 / 21

Advancing to step 4:
When dividing 129 by 21, we get 6 with a remainder of 3.
Use 6 as the next digit of our solution. 
Result so far: 136.0
If we take 126 away from 129, we end up with 3.
Include the next digit (6) from the dividend after 3, then repeat: 36 / 21

On to step 5:
36 divided by 21 is 1 with a remainder of 15.
The next digit of our result is 1. 
Result so far: 1361.0
Subtracting 21 from 36 leaves us with 15.
Grab the next digit (9) from the dividend, add it to 15, then carry on: 159 / 21

Going ahead to step 6:
21 goes into 159 7 times with a remainder of 12.
Write down 7 as next digit of the result. 
Result so far: 13617.0
If we subtract 147 from 159, we 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.

On to step 7:
21 goes into 120 5 times with a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 13617.5
Subtract 105 from 120 to 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.

Going ahead to step 8:
21 can be fit into 150 7 times, resulting in a remainder of 3.
The next digit of our result is 7. 
Result so far: 13617.57
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.

Advancing to step 9:
21 can be fit into 30 1 times, resulting in a remainder of 9.
The next digit of our result is 1. 
Result so far: 13617.571
If we take 21 away from 30, we end up with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Going ahead to step 10:
90 divided by 21 is 4 with a remainder of 6.
The next digit of our result is 4. 
Result so far: 13617.5714
The remainder is 6 after subtracting 84 from 90.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

On to step 11:
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: 13617.57142
If we subtract 42 from 60, we 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.

Advancing to step 12:
21 can be fit into 180 8 times, resulting in a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 13617.571428
Subtracting 168 from 180 leaves us with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Going ahead to step 13:
The number 21 fits into 120 5 times, leaving a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 13617.5714285
The remainder is 15 after subtracting 105 from 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Step 14:
The number 21 fits into 150 7 times, leaving a remainder of 3.
The number 7 becomes the next digit in our result. 
Result so far: 13617.57142857
If we take 147 away from 150, we end up with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

The quotient of the division is 13617.57142857, and the remainder is 3e-09.