We look at the division of 535726 by 21 
The aim is to understand the frequency of 21 in 535726.

Let's proceed to step 1:
The number 21 fits into 5 0 times, leaving a remainder of 5.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 5 to get 5.
Take the next digit (3) from the dividend and append it to 5, then repeat: 53 / 21

Advancing to step 2:
53 divided by 21 is 2 with a remainder of 11.
Use 2 as the next digit of our solution. 
Result so far: 2.0
Subtracting 42 from 53 leaves us with 11.
Bring next digit (5) of the dividend behind the 11 and repeat the process: 115 / 21

On to step 3:
The number 21 fits into 115 5 times, leaving a remainder of 10.
Write down 5 as next digit of the result. 
Result so far: 25.0
If we take 105 away from 115, we end up with 10.
Append the next digit (7) from the dividend to 10 and continue with: 107 / 21

Let's proceed to step 4:
21 goes into 107 5 times with a remainder of 2.
Put 5 as the next digit of the answer. 
Result so far: 255.0
The remainder is 2 after subtracting 105 from 107.
Fetch the next digit (2) from the dividend, attach it to 2 and continue: 22 / 21

Advancing to step 5:
If we divide 22 by 21, we get 1 and a remainder of 1.
Put 1 as the next digit of the answer. 
Result so far: 2551.0
Subtracting 21 from 22 leaves us with 1.
Fetch the next digit (6) from the dividend, attach it to 1 and continue: 16 / 21

Moving on to step 6:
If we divide 16 by 21, we get 0 and a remainder of 16.
The next digit of our result is 0. 
Result so far: 25510.0
If we subtract 0 from 16, 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.

On to step 7:
21 goes into 160 7 times with a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 25510.7
If we subtract 147 from 160, we get 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 8:
21 goes into 130 6 times with a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 25510.76
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 9:
40 divided by 21 is 1 with a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 25510.761
Subtract 21 from 40 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Going ahead to step 10:
If we divide 190 by 21, we get 9 and a remainder of 1.
The next digit of our result is 9. 
Result so far: 25510.7619
If we take 189 away from 190, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Step 11:
21 goes into 10 0 times with a remainder of 10.
Write down 0 as next digit of the result. 
Result so far: 25510.7619
Subtracting 0 from 10 leaves us with 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 12:
The number 21 fits into 100 4 times, leaving a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 25510.761904
Subtract 84 from 100 to 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 13:
21 goes into 160 7 times with a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 25510.7619047
Subtract 147 from 160 to get 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Moving on to step 14:
If we divide 130 by 21, we get 6 and a remainder of 4.
The next digit of our result is 6. 
Result so far: 25510.76190476
If we subtract 126 from 130, we get 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

The quotient of the division is 25510.76190476, and the remainder is 4e-09.