445439 ÷ 21 
The aim is to understand the frequency of 21 in 445439.

Advancing to step 1:
When dividing 4 by 21, we get 0 with a remainder of 4.
The next digit of our result is 0. 
Result so far: 0.0
If we subtract 0 from 4, we get 4.
Take the next digit (4) from the dividend and append it to 4, then repeat: 44 / 21

Going ahead to step 2:
21 can be fit into 44 2 times, resulting in a remainder of 2.
Use 2 as the next digit of our solution. 
Result so far: 2.0
Deduct 42 from 44 and we're left with 2.
Fetch the next digit (5) from the dividend, attach it to 2 and continue: 25 / 21

Let's proceed to step 3:
25 divided by 21 is 1 with a remainder of 4.
Write down 1 as next digit of the result. 
Result so far: 21.0
Subtracting 21 from 25 leaves us with 4.
Fetch the next digit (4) from the dividend, attach it to 4 and continue: 44 / 21

Going ahead to step 4:
If we divide 44 by 21, we get 2 and a remainder of 2.
Use 2 as the next digit of our solution. 
Result so far: 212.0
Subtract 42 from 44 to get 2.
Grab the next digit (3) from the dividend, add it to 2, then carry on: 23 / 21

Moving on to step 5:
21 can be fit into 23 1 times, resulting in a remainder of 2.
The next digit of our result is 1. 
Result so far: 2121.0
Subtracting 21 from 23 leaves us with 2.
Fetch the next digit (9) from the dividend, attach it to 2 and continue: 29 / 21

Step 6:
21 can be fit into 29 1 times, resulting in a remainder of 8.
Write down 1 as next digit of the result. 
Result so far: 21211.0
If we take 21 away from 29, 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 7:
80 divided by 21 is 3 with a remainder of 17.
Put 3 as the next digit of the answer. 
Result so far: 21211.3
If we take 63 away from 80, we end up 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.

On to step 8:
When dividing 170 by 21, we get 8 with a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 21211.38
Subtract 168 from 170 to get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Advancing to step 9:
The number 21 fits into 20 0 times, leaving a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 21211.38
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.

Let's proceed to step 10:
If we divide 200 by 21, we get 9 and a remainder of 11.
The next digit of our result is 9. 
Result so far: 21211.3809
Subtract 189 from 200 to 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 11:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Put 5 as the next digit of the answer. 
Result so far: 21211.38095
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.

On to step 12:
21 can be fit into 50 2 times, resulting in a remainder of 8.
Use 2 as the next digit of our solution. 
Result so far: 21211.380952
The remainder is 8 after subtracting 42 from 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Advancing to step 13:
The number 21 fits into 80 3 times, leaving a remainder of 17.
Use 3 as the next digit of our solution. 
Result so far: 21211.3809523
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.

Going ahead to step 14:
21 goes into 170 8 times with a remainder of 2.
Write down 8 as next digit of the result. 
Result so far: 21211.38095238
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.

The quotient of the division is 21211.38095238, and the remainder is 2e-09.