901501 ÷ 21 
The aim is to understand the frequency of 21 in 901501.

Going ahead to step 1:
21 can be fit into 9 0 times, resulting in a remainder of 9.
Write down 0 as next digit of the result. 
Result so far: 0.0
The remainder is 9 after subtracting 0 from 9.
Grab the next digit (0) from the dividend, add it to 9, then carry on: 90 / 21

Going ahead to step 2:
90 divided by 21 is 4 with a remainder of 6.
Write down 4 as next digit of the result. 
Result so far: 4.0
Subtracting 84 from 90 leaves us with 6.
Grab the next digit (1) from the dividend, add it to 6, then carry on: 61 / 21

On to step 3:
61 divided by 21 is 2 with a remainder of 19.
The number 2 becomes the next digit in our result. 
Result so far: 42.0
Subtract 42 from 61 to get 19.
Include the next digit (5) from the dividend after 19, then repeat: 195 / 21

Step 4:
The number 21 fits into 195 9 times, leaving a remainder of 6.
Record the quotient 9 as the next digit in the result. 
Result so far: 429.0
The remainder is 6 after subtracting 189 from 195.
Include the next digit (0) from the dividend after 6, then repeat: 60 / 21

Step 5:
If we divide 60 by 21, we get 2 and a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 4292.0
Deduct 42 from 60 and we're left with 18.
Append the next digit (1) from the dividend to 18 and continue with: 181 / 21

On to step 6:
When dividing 181 by 21, we get 8 with a remainder of 13.
Record the quotient 8 as the next digit in the result. 
Result so far: 42928.0
If we subtract 168 from 181, 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 7:
21 goes into 130 6 times with a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 42928.6
The remainder is 4 after subtracting 126 from 130.
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 8:
21 can be fit into 40 1 times, resulting in a remainder of 19.
Use 1 as the next digit of our solution. 
Result so far: 42928.61
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.

Step 9:
21 goes into 190 9 times with a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 42928.619
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.

Going ahead to step 10:
If we divide 10 by 21, we get 0 and a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 42928.619
The remainder is 10 after subtracting 0 from 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 11:
21 goes into 100 4 times with a remainder of 16.
The next digit of our result is 4. 
Result so far: 42928.61904
Deduct 84 from 100 and we're left 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.

Step 12:
21 can be fit into 160 7 times, resulting in a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 42928.619047
If we take 147 away from 160, we end up with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Step 13:
The number 21 fits into 130 6 times, leaving a remainder of 4.
Record the quotient 6 as the next digit in the result. 
Result so far: 42928.6190476
Subtract 126 from 130 to 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.

Going ahead to step 14:
40 divided by 21 is 1 with a remainder of 19.
The next digit of our result is 1. 
Result so far: 42928.61904761
Deduct 21 from 40 and we're left 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.

In conclusion, the division gives 42928.61904761 with a balance of 1.9e-08.