We divide 645429 by 21
The aim is to understand the frequency of 21 in 645429.

Advancing to step 1:
21 goes into 6 0 times with a remainder of 6.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we subtract 0 from 6, we get 6.
Bring next digit (4) of the dividend behind the 6 and repeat the process: 64 / 21

Going ahead to step 2:
21 can be fit into 64 3 times, resulting in a remainder of 1.
The number 3 becomes the next digit in our result. 
Result so far: 3.0
Subtracting 63 from 64 leaves us with 1.
Append the next digit (5) from the dividend to 1 and continue with: 15 / 21

Advancing to step 3:
If we divide 15 by 21, we get 0 and a remainder of 15.
The number 0 becomes the next digit in our result. 
Result so far: 30.0
Deduct 0 from 15 and we're left with 15.
Append the next digit (4) from the dividend to 15 and continue with: 154 / 21

Going ahead to step 4:
When dividing 154 by 21, we get 7 with a remainder of 7.
The next digit of our result is 7. 
Result so far: 307.0
If we subtract 147 from 154, we get 7.
Fetch the next digit (2) from the dividend, attach it to 7 and continue: 72 / 21

On to step 5:
The number 21 fits into 72 3 times, leaving a remainder of 9.
Record the quotient 3 as the next digit in the result. 
Result so far: 3073.0
If we subtract 63 from 72, we get 9.
Take the next digit (9) from the dividend and append it to 9, then repeat: 99 / 21

On to step 6:
21 goes into 99 4 times with a remainder of 15.
The next digit of our result is 4. 
Result so far: 30734.0
Subtract 84 from 99 to get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Going ahead to step 7:
When dividing 150 by 21, we get 7 with a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 30734.7
Deduct 147 from 150 and we're left with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Advancing to step 8:
21 goes into 30 1 times with a remainder of 9.
The next digit of our result is 1. 
Result so far: 30734.71
Subtracting 21 from 30 leaves us with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Advancing to step 9:
When dividing 90 by 21, we get 4 with a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 30734.714
Subtracting 84 from 90 leaves us with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Moving on to step 10:
When dividing 60 by 21, we get 2 with a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 30734.7142
Deduct 42 from 60 and we're left with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Advancing to step 11:
180 divided by 21 is 8 with a remainder of 12.
The next digit of our result is 8. 
Result so far: 30734.71428
Subtract 168 from 180 to get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

On to step 12:
If we divide 120 by 21, we get 5 and a remainder of 15.
Write down 5 as next digit of the result. 
Result so far: 30734.714285
The remainder is 15 after subtracting 105 from 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Moving on to step 13:
If we divide 150 by 21, we get 7 and a remainder of 3.
The next digit of our result is 7. 
Result so far: 30734.7142857
The remainder is 3 after subtracting 147 from 150.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Let's proceed to step 14:
21 can be fit into 30 1 times, resulting in a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 30734.71428571
Subtract 21 from 30 to get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

The quotient of the division is 30734.71428571, and the remainder is 9e-09.