209537 divided by 21 
The aim is to understand the frequency of 21 in 209537.

Advancing to step 1:
If we divide 2 by 21, we get 0 and a remainder of 2.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we take 0 away from 2, we end up with 2.
Take the next digit (0) from the dividend and append it to 2, then repeat: 20 / 21

Advancing to step 2:
21 can be fit into 20 0 times, resulting in a remainder of 20.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 20, we end up with 20.
Grab the next digit (9) from the dividend, add it to 20, then carry on: 209 / 21

Advancing to step 3:
If we divide 209 by 21, we get 9 and a remainder of 20.
Use 9 as the next digit of our solution. 
Result so far: 9.0
If we take 189 away from 209, we end up with 20.
Fetch the next digit (5) from the dividend, attach it to 20 and continue: 205 / 21

Step 4:
205 divided by 21 is 9 with a remainder of 16.
Use 9 as the next digit of our solution. 
Result so far: 99.0
If we take 189 away from 205, we end up with 16.
Bring next digit (3) of the dividend behind the 16 and repeat the process: 163 / 21

On to step 5:
If we divide 163 by 21, we get 7 and a remainder of 16.
Write down 7 as next digit of the result. 
Result so far: 997.0
The remainder is 16 after subtracting 147 from 163.
Take the next digit (7) from the dividend and append it to 16, then repeat: 167 / 21

Moving on to step 6:
The number 21 fits into 167 7 times, leaving a remainder of 20.
Put 7 as the next digit of the answer. 
Result so far: 9977.0
Deduct 147 from 167 and we're left 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.

Advancing to step 7:
The number 21 fits into 200 9 times, leaving a remainder of 11.
Put 9 as the next digit of the answer. 
Result so far: 9977.9
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.

Going ahead to step 8:
The number 21 fits into 110 5 times, leaving a remainder of 5.
Put 5 as the next digit of the answer. 
Result so far: 9977.95
Deduct 105 from 110 and we're left with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

On to step 9:
The number 21 fits into 50 2 times, leaving a remainder of 8.
The next digit of our result is 2. 
Result so far: 9977.952
Subtract 42 from 50 to 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.

Going ahead to step 10:
80 divided by 21 is 3 with a remainder of 17.
Put 3 as the next digit of the answer. 
Result so far: 9977.9523
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.

Step 11:
If we divide 170 by 21, we get 8 and a remainder of 2.
The next digit of our result is 8. 
Result so far: 9977.95238
The remainder is 2 after subtracting 168 from 170.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Going ahead to step 12:
21 goes into 20 0 times with a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 9977.95238
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.

Let's proceed to step 13:
21 goes into 200 9 times with a remainder of 11.
The number 9 becomes the next digit in our result. 
Result so far: 9977.9523809
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.

Advancing to step 14:
21 goes into 110 5 times with a remainder of 5.
Put 5 as the next digit of the answer. 
Result so far: 9977.95238095
Deduct 105 from 110 and we're left with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Our division results in 9977.95238095 with a remaining 5e-09.