528641 ÷ 21 
The aim is to understand the frequency of 21 in 528641.

Let's proceed to step 1:
5 divided by 21 is 0 with a remainder of 5.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtracting 0 from 5 leaves us with 5.
Take the next digit (2) from the dividend and append it to 5, then repeat: 52 / 21

Moving on to step 2:
The number 21 fits into 52 2 times, leaving a remainder of 10.
Put 2 as the next digit of the answer. 
Result so far: 2.0
If we take 42 away from 52, we end up with 10.
Bring next digit (8) of the dividend behind the 10 and repeat the process: 108 / 21

Step 3:
When dividing 108 by 21, we get 5 with a remainder of 3.
Use 5 as the next digit of our solution. 
Result so far: 25.0
The remainder is 3 after subtracting 105 from 108.
Bring next digit (6) of the dividend behind the 3 and repeat the process: 36 / 21

Step 4:
When dividing 36 by 21, we get 1 with a remainder of 15.
Record the quotient 1 as the next digit in the result. 
Result so far: 251.0
The remainder is 15 after subtracting 21 from 36.
Grab the next digit (4) from the dividend, add it to 15, then carry on: 154 / 21

Going ahead to step 5:
The number 21 fits into 154 7 times, leaving a remainder of 7.
Use 7 as the next digit of our solution. 
Result so far: 2517.0
Deduct 147 from 154 and we're left with 7.
Take the next digit (1) from the dividend and append it to 7, then repeat: 71 / 21

Advancing to step 6:
21 can be fit into 71 3 times, resulting in a remainder of 8.
The next digit of our result is 3. 
Result so far: 25173.0
The remainder is 8 after subtracting 63 from 71.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Step 7:
21 can be fit into 80 3 times, resulting in a remainder of 17.
Record the quotient 3 as the next digit in the result. 
Result so far: 25173.3
Subtract 63 from 80 to get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Advancing to step 8:
If we divide 170 by 21, we get 8 and a remainder of 2.
Put 8 as the next digit of the answer. 
Result so far: 25173.38
Subtract 168 from 170 to get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Let's proceed to step 9:
21 goes into 20 0 times with a remainder of 20.
The next digit of our result is 0. 
Result so far: 25173.38
The remainder is 20 after subtracting 0 from 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Moving on to step 10:
If we divide 200 by 21, we get 9 and a remainder of 11.
Use 9 as the next digit of our solution. 
Result so far: 25173.3809
Deduct 189 from 200 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.

Step 11:
21 goes into 110 5 times with a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 25173.38095
If we subtract 105 from 110, we 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 12:
21 goes into 50 2 times with a remainder of 8.
Record the quotient 2 as the next digit in the result. 
Result so far: 25173.380952
If we subtract 42 from 50, we get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Step 13:
The number 21 fits into 80 3 times, leaving a remainder of 17.
The next digit of our result is 3. 
Result so far: 25173.3809523
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.

Going ahead to step 14:
170 divided by 21 is 8 with a remainder of 2.
The next digit of our result is 8. 
Result so far: 25173.38095238
If we subtract 168 from 170, we get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Our division results in 25173.38095238 with a remaining 2e-09.