501967 ÷ 21 
The aim is to understand the frequency of 21 in 501967.

Moving on to step 1:
21 goes into 5 0 times with a remainder of 5.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 5, we end up with 5.
Take the next digit (0) from the dividend and append it to 5, then repeat: 50 / 21

Let's proceed to step 2:
If we divide 50 by 21, we get 2 and a remainder of 8.
Put 2 as the next digit of the answer. 
Result so far: 2.0
If we subtract 42 from 50, we get 8.
Fetch the next digit (1) from the dividend, attach it to 8 and continue: 81 / 21

Let's proceed to step 3:
21 goes into 81 3 times with a remainder of 18.
Use 3 as the next digit of our solution. 
Result so far: 23.0
Subtracting 63 from 81 leaves us with 18.
Bring next digit (9) of the dividend behind the 18 and repeat the process: 189 / 21

On to step 4:
If we divide 189 by 21, we get 9 and a remainder of 0.
Record the quotient 9 as the next digit in the result. 
Result so far: 239.0
The remainder is 0 after subtracting 189 from 189.
Include the next digit (6) from the dividend after 0, then repeat: 6 / 21

On to step 5:
21 goes into 6 0 times with a remainder of 6.
Write down 0 as next digit of the result. 
Result so far: 2390.0
If we take 0 away from 6, we end up with 6.
Append the next digit (7) from the dividend to 6 and continue with: 67 / 21

Going ahead to step 6:
67 divided by 21 is 3 with a remainder of 4.
Write down 3 as next digit of the result. 
Result so far: 23903.0
Subtracting 63 from 67 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.

Going ahead to step 7:
40 divided by 21 is 1 with a remainder of 19.
The number 1 becomes the next digit in our result. 
Result so far: 23903.1
Subtracting 21 from 40 leaves us with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Let's proceed to step 8:
21 goes into 190 9 times with a remainder of 1.
Put 9 as the next digit of the answer. 
Result so far: 23903.19
Deduct 189 from 190 and we're left 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 9:
21 can be fit into 10 0 times, resulting in a remainder of 10.
Record the quotient 0 as the next digit in the result. 
Result so far: 23903.19
Deduct 0 from 10 and we're left 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.

Let's proceed to step 10:
21 goes into 100 4 times with a remainder of 16.
The next digit of our result is 4. 
Result so far: 23903.1904
Subtracting 84 from 100 leaves us with 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 11:
If we divide 160 by 21, we get 7 and a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 23903.19047
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.

Going ahead to step 12:
When dividing 130 by 21, we get 6 with a remainder of 4.
Write down 6 as next digit of the result. 
Result so far: 23903.190476
If we take 126 away from 130, we end up 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.

Advancing to step 13:
If we divide 40 by 21, we get 1 and a remainder of 19.
Use 1 as the next digit of our solution. 
Result so far: 23903.1904761
If we take 21 away from 40, we end up with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Moving on to step 14:
21 goes into 190 9 times with a remainder of 1.
Record the quotient 9 as the next digit in the result. 
Result so far: 23903.19047619
Deduct 189 from 190 and we're left 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.

The final outcome is 23903.19047619, with a leftover of 1e-09.