583873 divided by 21 
The aim is to understand the frequency of 21 in 583873.

Advancing to step 1:
21 goes into 5 0 times with a remainder of 5.
Put 0 as the next digit of the answer. 
Result so far: 0.0
The remainder is 5 after subtracting 0 from 5.
Append the next digit (8) from the dividend to 5 and continue with: 58 / 21

Advancing to step 2:
If we divide 58 by 21, we get 2 and a remainder of 16.
The number 2 becomes the next digit in our result. 
Result so far: 2.0
Subtract 42 from 58 to get 16.
Grab the next digit (3) from the dividend, add it to 16, then carry on: 163 / 21

Moving on to step 3:
163 divided by 21 is 7 with a remainder of 16.
Put 7 as the next digit of the answer. 
Result so far: 27.0
Subtracting 147 from 163 leaves us with 16.
Take the next digit (8) from the dividend and append it to 16, then repeat: 168 / 21

On to step 4:
21 goes into 168 8 times with a remainder of 0.
Record the quotient 8 as the next digit in the result. 
Result so far: 278.0
The remainder is 0 after subtracting 168 from 168.
Grab the next digit (7) from the dividend, add it to 0, then carry on: 7 / 21

Moving on to step 5:
7 divided by 21 is 0 with a remainder of 7.
Use 0 as the next digit of our solution. 
Result so far: 2780.0
Subtract 0 from 7 to get 7.
Include the next digit (3) from the dividend after 7, then repeat: 73 / 21

Advancing to step 6:
The number 21 fits into 73 3 times, leaving a remainder of 10.
Put 3 as the next digit of the answer. 
Result so far: 27803.0
Subtracting 63 from 73 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.

Let's proceed to step 7:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Put 4 as the next digit of the answer. 
Result so far: 27803.4
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.

Step 8:
If we divide 160 by 21, we get 7 and a remainder of 13.
The number 7 becomes the next digit in our result. 
Result so far: 27803.47
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.

Step 9:
If we divide 130 by 21, we get 6 and a remainder of 4.
Record the quotient 6 as the next digit in the result. 
Result so far: 27803.476
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.

Step 10:
21 goes into 40 1 times with a remainder of 19.
Put 1 as the next digit of the answer. 
Result so far: 27803.4761
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.

Let's proceed to step 11:
If we divide 190 by 21, we get 9 and a remainder of 1.
Use 9 as the next digit of our solution. 
Result so far: 27803.47619
Subtracting 189 from 190 leaves us 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.

Let's proceed to step 12:
21 can be fit into 10 0 times, resulting in a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 27803.47619
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.

Going ahead to step 13:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Put 4 as the next digit of the answer. 
Result so far: 27803.4761904
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.

Let's proceed to step 14:
If we divide 160 by 21, we get 7 and a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 27803.47619047
Subtracting 147 from 160 leaves us 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.

After the division, we end up with 27803.47619047 and a remainder of 1.3e-08.