201002 divided by 21 
The aim is to understand the frequency of 21 in 201002.

On to step 1:
21 goes into 2 0 times with a remainder of 2.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtracting 0 from 2 leaves us with 2.
Append the next digit (0) from the dividend to 2 and continue with: 20 / 21

Moving on to step 2:
If we divide 20 by 21, we get 0 and a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we subtract 0 from 20, we get 20.
Fetch the next digit (1) from the dividend, attach it to 20 and continue: 201 / 21

Advancing to step 3:
21 goes into 201 9 times with a remainder of 12.
The next digit of our result is 9. 
Result so far: 9.0
Subtracting 189 from 201 leaves us with 12.
Include the next digit (0) from the dividend after 12, then repeat: 120 / 21

On to step 4:
21 can be fit into 120 5 times, resulting in a remainder of 15.
Use 5 as the next digit of our solution. 
Result so far: 95.0
The remainder is 15 after subtracting 105 from 120.
Fetch the next digit (0) from the dividend, attach it to 15 and continue: 150 / 21

Advancing to step 5:
21 can be fit into 150 7 times, resulting in a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 957.0
The remainder is 3 after subtracting 147 from 150.
Grab the next digit (2) from the dividend, add it to 3, then carry on: 32 / 21

Let's proceed to step 6:
21 can be fit into 32 1 times, resulting in a remainder of 11.
Use 1 as the next digit of our solution. 
Result so far: 9571.0
Deduct 21 from 32 and we're left with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Let's proceed to step 7:
When dividing 110 by 21, we get 5 with a remainder of 5.
The number 5 becomes the next digit in our result. 
Result so far: 9571.5
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.

Step 8:
50 divided by 21 is 2 with a remainder of 8.
Put 2 as the next digit of the answer. 
Result so far: 9571.52
The remainder is 8 after subtracting 42 from 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Going ahead to step 9:
21 goes into 80 3 times with a remainder of 17.
Write down 3 as next digit of the result. 
Result so far: 9571.523
Deduct 63 from 80 and we're left 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.

On to step 10:
21 can be fit into 170 8 times, resulting in a remainder of 2.
Record the quotient 8 as the next digit in the result. 
Result so far: 9571.5238
If we take 168 away from 170, we end up with 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 11:
21 goes into 20 0 times with a remainder of 20.
Record the quotient 0 as the next digit in the result. 
Result so far: 9571.5238
Subtracting 0 from 20 leaves us 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.

Let's proceed to step 12:
21 goes into 200 9 times with a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 9571.523809
Subtracting 189 from 200 leaves us with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Going ahead to step 13:
If we divide 110 by 21, we get 5 and a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 9571.5238095
The remainder is 5 after subtracting 105 from 110.
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 14:
50 divided by 21 is 2 with a remainder of 8.
Record the quotient 2 as the next digit in the result. 
Result so far: 9571.52380952
If we take 42 away from 50, we end up 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.

The final outcome is 9571.52380952, with a leftover of 8e-09.