624739 ÷ 21 
The aim is to understand the frequency of 21 in 624739.

Step 1:
The number 21 fits into 6 0 times, leaving a remainder of 6.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we subtract 0 from 6, we get 6.
Take the next digit (2) from the dividend and append it to 6, then repeat: 62 / 21

On to step 2:
21 goes into 62 2 times with a remainder of 20.
Put 2 as the next digit of the answer. 
Result so far: 2.0
Subtracting 42 from 62 leaves us with 20.
Take the next digit (4) from the dividend and append it to 20, then repeat: 204 / 21

Advancing to step 3:
204 divided by 21 is 9 with a remainder of 15.
The number 9 becomes the next digit in our result. 
Result so far: 29.0
If we take 189 away from 204, we end up with 15.
Bring next digit (7) of the dividend behind the 15 and repeat the process: 157 / 21

Step 4:
157 divided by 21 is 7 with a remainder of 10.
Put 7 as the next digit of the answer. 
Result so far: 297.0
If we subtract 147 from 157, we get 10.
Append the next digit (3) from the dividend to 10 and continue with: 103 / 21

Let's proceed to step 5:
103 divided by 21 is 4 with a remainder of 19.
Use 4 as the next digit of our solution. 
Result so far: 2974.0
If we take 84 away from 103, we end up with 19.
Append the next digit (9) from the dividend to 19 and continue with: 199 / 21

Let's proceed to step 6:
If we divide 199 by 21, we get 9 and a remainder of 10.
Put 9 as the next digit of the answer. 
Result so far: 29749.0
If we subtract 189 from 199, we get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Advancing to step 7:
When dividing 100 by 21, we get 4 with a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 29749.4
If we subtract 84 from 100, we get 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

On to step 8:
160 divided by 21 is 7 with a remainder of 13.
The next digit of our result is 7. 
Result so far: 29749.47
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.

Going ahead to step 9:
21 can be fit into 130 6 times, resulting in a remainder of 4.
Write down 6 as next digit of the result. 
Result so far: 29749.476
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.

Advancing to step 10:
The number 21 fits into 40 1 times, leaving a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 29749.4761
If we take 21 away from 40, we end up 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.

On to step 11:
21 goes into 190 9 times with a remainder of 1.
Write down 9 as next digit of the result. 
Result so far: 29749.47619
If we subtract 189 from 190, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

On to step 12:
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: 29749.47619
Deduct 0 from 10 and we're left 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 13:
If we divide 100 by 21, we get 4 and a remainder of 16.
Record the quotient 4 as the next digit in the result. 
Result so far: 29749.4761904
The remainder is 16 after subtracting 84 from 100.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Advancing to step 14:
The number 21 fits into 160 7 times, leaving a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 29749.47619047
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.

The final outcome is 29749.47619047, with a leftover of 1.3e-08.