Let's divide 213678 by 21
The aim is to understand the frequency of 21 in 213678.

Going ahead to step 1:
2 divided by 21 is 0 with a remainder of 2.
Use 0 as the next digit of our solution. 
Result so far: 0.0
The remainder is 2 after subtracting 0 from 2.
Fetch the next digit (1) from the dividend, attach it to 2 and continue: 21 / 21

Going ahead to step 2:
The number 21 fits into 21 1 times, leaving a remainder of 0.
Put 1 as the next digit of the answer. 
Result so far: 1.0
If we subtract 21 from 21, we get 0.
Grab the next digit (3) from the dividend, add it to 0, then carry on: 3 / 21

On to step 3:
The number 21 fits into 3 0 times, leaving a remainder of 3.
Use 0 as the next digit of our solution. 
Result so far: 10.0
The remainder is 3 after subtracting 0 from 3.
Append the next digit (6) from the dividend to 3 and continue with: 36 / 21

On to step 4:
36 divided by 21 is 1 with a remainder of 15.
The next digit of our result is 1. 
Result so far: 101.0
If we take 21 away from 36, we end up with 15.
Include the next digit (7) from the dividend after 15, then repeat: 157 / 21

Going ahead to step 5:
21 can be fit into 157 7 times, resulting in a remainder of 10.
The number 7 becomes the next digit in our result. 
Result so far: 1017.0
Deduct 147 from 157 and we're left with 10.
Include the next digit (8) from the dividend after 10, then repeat: 108 / 21

On to step 6:
The number 21 fits into 108 5 times, leaving a remainder of 3.
The number 5 becomes the next digit in our result. 
Result so far: 10175.0
The remainder is 3 after subtracting 105 from 108.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Moving on to step 7:
30 divided by 21 is 1 with a remainder of 9.
Record the quotient 1 as the next digit in the result. 
Result so far: 10175.1
Subtract 21 from 30 to get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Let's proceed to step 8:
21 can be fit into 90 4 times, resulting in a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 10175.14
Subtract 84 from 90 to get 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Moving on to step 9:
60 divided by 21 is 2 with a remainder of 18.
Put 2 as the next digit of the answer. 
Result so far: 10175.142
Subtracting 42 from 60 leaves us with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Step 10:
180 divided by 21 is 8 with a remainder of 12.
Put 8 as the next digit of the answer. 
Result so far: 10175.1428
Deduct 168 from 180 and we're left 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 11:
21 goes into 120 5 times with a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 10175.14285
Deduct 105 from 120 and we're left with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Let's proceed to step 12:
21 can be fit into 150 7 times, resulting in a remainder of 3.
Record the quotient 7 as the next digit in the result. 
Result so far: 10175.142857
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.

Moving on to step 13:
21 can be fit into 30 1 times, resulting in a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 10175.1428571
The remainder is 9 after subtracting 21 from 30.
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 14:
If we divide 90 by 21, we get 4 and a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 10175.14285714
Subtracting 84 from 90 leaves us with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

The final outcome is 10175.14285714, with a leftover of 6e-09.