903587 divided by 21 
The aim is to understand the frequency of 21 in 903587.

Let's proceed to step 1:
21 goes into 9 0 times with a remainder of 9.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtract 0 from 9 to get 9.
Include the next digit (0) from the dividend after 9, then repeat: 90 / 21

Advancing to step 2:
90 divided by 21 is 4 with a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 4.0
If we subtract 84 from 90, we get 6.
Take the next digit (3) from the dividend and append it to 6, then repeat: 63 / 21

Moving on to step 3:
63 divided by 21 is 3 with a remainder of 0.
Record the quotient 3 as the next digit in the result. 
Result so far: 43.0
The remainder is 0 after subtracting 63 from 63.
Bring next digit (5) of the dividend behind the 0 and repeat the process: 5 / 21

Let's proceed to step 4:
5 divided by 21 is 0 with a remainder of 5.
The number 0 becomes the next digit in our result. 
Result so far: 430.0
The remainder is 5 after subtracting 0 from 5.
Take the next digit (8) from the dividend and append it to 5, then repeat: 58 / 21

Going ahead to step 5:
21 can be fit into 58 2 times, resulting in a remainder of 16.
The next digit of our result is 2. 
Result so far: 4302.0
If we subtract 42 from 58, we get 16.
Grab the next digit (7) from the dividend, add it to 16, then carry on: 167 / 21

On to step 6:
21 goes into 167 7 times with a remainder of 20.
The number 7 becomes the next digit in our result. 
Result so far: 43027.0
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:
200 divided by 21 is 9 with a remainder of 11.
Record the quotient 9 as the next digit in the result. 
Result so far: 43027.9
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.

Step 8:
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: 43027.95
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.

Advancing to step 9:
When dividing 50 by 21, we get 2 with a remainder of 8.
The next digit of our result is 2. 
Result so far: 43027.952
If we take 42 away from 50, we end up with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

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: 43027.9523
Subtract 63 from 80 to 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.

Step 11:
If we divide 170 by 21, we get 8 and a remainder of 2.
Put 8 as the next digit of the answer. 
Result so far: 43027.95238
Deduct 168 from 170 and we're left 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.

Let's proceed to step 12:
If we divide 20 by 21, we get 0 and a remainder of 20.
Record the quotient 0 as the next digit in the result. 
Result so far: 43027.95238
If we take 0 away from 20, we end up 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.

Going ahead to step 13:
200 divided by 21 is 9 with a remainder of 11.
Use 9 as the next digit of our solution. 
Result so far: 43027.9523809
If we take 189 away from 200, we end up 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.

Step 14:
110 divided by 21 is 5 with a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 43027.95238095
The remainder is 5 after subtracting 105 from 110.
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 43027.95238095 with a remaining 5e-09.