We divide 953993 by 21
The aim is to understand the frequency of 21 in 953993.

Let's proceed to step 1:
When dividing 9 by 21, we get 0 with a remainder of 9.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtract 0 from 9 to get 9.
Fetch the next digit (5) from the dividend, attach it to 9 and continue: 95 / 21

Step 2:
21 goes into 95 4 times with a remainder of 11.
Write down 4 as next digit of the result. 
Result so far: 4.0
Subtract 84 from 95 to get 11.
Grab the next digit (3) from the dividend, add it to 11, then carry on: 113 / 21

On to step 3:
21 goes into 113 5 times with a remainder of 8.
Record the quotient 5 as the next digit in the result. 
Result so far: 45.0
The remainder is 8 after subtracting 105 from 113.
Append the next digit (9) from the dividend to 8 and continue with: 89 / 21

Moving on to step 4:
21 goes into 89 4 times with a remainder of 5.
Use 4 as the next digit of our solution. 
Result so far: 454.0
Deduct 84 from 89 and we're left with 5.
Append the next digit (9) from the dividend to 5 and continue with: 59 / 21

Advancing to step 5:
59 divided by 21 is 2 with a remainder of 17.
Use 2 as the next digit of our solution. 
Result so far: 4542.0
Deduct 42 from 59 and we're left with 17.
Fetch the next digit (3) from the dividend, attach it to 17 and continue: 173 / 21

Moving on to step 6:
If we divide 173 by 21, we get 8 and a remainder of 5.
Write down 8 as next digit of the result. 
Result so far: 45428.0
Subtracting 168 from 173 leaves us 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.

Step 7:
21 can be fit into 50 2 times, resulting in a remainder of 8.
Record the quotient 2 as the next digit in the result. 
Result so far: 45428.2
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.

Moving on to step 8:
If we divide 80 by 21, we get 3 and a remainder of 17.
Record the quotient 3 as the next digit in the result. 
Result so far: 45428.23
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.

Moving on to step 9:
If we divide 170 by 21, we get 8 and a remainder of 2.
Record the quotient 8 as the next digit in the result. 
Result so far: 45428.238
If we take 168 away from 170, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Moving on to step 10:
If we divide 20 by 21, we get 0 and a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 45428.238
Subtracting 0 from 20 leaves us 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.

Moving on to step 11:
21 goes into 200 9 times with a remainder of 11.
The next digit of our result is 9. 
Result so far: 45428.23809
If we subtract 189 from 200, we get 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Moving on to step 12:
When dividing 110 by 21, we get 5 with a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 45428.238095
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.

Going ahead to step 13:
The number 21 fits into 50 2 times, leaving a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 45428.2380952
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.

Moving on to step 14:
When dividing 80 by 21, we get 3 with a remainder of 17.
The next digit of our result is 3. 
Result so far: 45428.23809523
If we subtract 63 from 80, we 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.

The final outcome is 45428.23809523, with a leftover of 1.7e-08.