We look at the division of 897865 by 21 
The aim is to understand the frequency of 21 in 897865.

Advancing to step 1:
The number 21 fits into 8 0 times, leaving a remainder of 8.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 8, we end up with 8.
Grab the next digit (9) from the dividend, add it to 8, then carry on: 89 / 21

Advancing to step 2:
If we divide 89 by 21, we get 4 and a remainder of 5.
Write down 4 as next digit of the result. 
Result so far: 4.0
If we subtract 84 from 89, we get 5.
Take the next digit (7) from the dividend and append it to 5, then repeat: 57 / 21

On to step 3:
57 divided by 21 is 2 with a remainder of 15.
Use 2 as the next digit of our solution. 
Result so far: 42.0
The remainder is 15 after subtracting 42 from 57.
Append the next digit (8) from the dividend to 15 and continue with: 158 / 21

Step 4:
If we divide 158 by 21, we get 7 and a remainder of 11.
Use 7 as the next digit of our solution. 
Result so far: 427.0
If we take 147 away from 158, we end up with 11.
Bring next digit (6) of the dividend behind the 11 and repeat the process: 116 / 21

On to step 5:
If we divide 116 by 21, we get 5 and a remainder of 11.
Use 5 as the next digit of our solution. 
Result so far: 4275.0
Subtract 105 from 116 to get 11.
Bring next digit (5) of the dividend behind the 11 and repeat the process: 115 / 21

Step 6:
The number 21 fits into 115 5 times, leaving a remainder of 10.
Use 5 as the next digit of our solution. 
Result so far: 42755.0
Subtract 105 from 115 to 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.

Step 7:
When dividing 100 by 21, we get 4 with a remainder of 16.
Put 4 as the next digit of the answer. 
Result so far: 42755.4
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.

Let's proceed to step 8:
When dividing 160 by 21, we get 7 with a remainder of 13.
Use 7 as the next digit of our solution. 
Result so far: 42755.47
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.

Let's proceed to step 9:
21 goes into 130 6 times with a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 42755.476
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 10:
21 goes into 40 1 times with a remainder of 19.
Write down 1 as next digit of the result. 
Result so far: 42755.4761
Subtracting 21 from 40 leaves us with 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 11:
190 divided by 21 is 9 with a remainder of 1.
Put 9 as the next digit of the answer. 
Result so far: 42755.47619
If we subtract 189 from 190, 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.

Advancing to step 12:
21 goes into 10 0 times with a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 42755.47619
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.

Going ahead to step 13:
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: 42755.4761904
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.

Step 14:
If we divide 160 by 21, we get 7 and a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 42755.47619047
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.

After the division, we end up with 42755.47619047 and a remainder of 1.3e-08.