We look at the division of 53615155 by 21 
The aim is to understand the frequency of 21 in 53615155.

Moving on to step 1:
21 can be fit into 5 0 times, resulting in a remainder of 5.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 5, we end up with 5.
Take the next digit (3) from the dividend and append it to 5, then repeat: 53 / 21

Let's proceed to step 2:
21 can be fit into 53 2 times, resulting in a remainder of 11.
Use 2 as the next digit of our solution. 
Result so far: 2.0
Subtract 42 from 53 to get 11.
Bring next digit (6) of the dividend behind the 11 and repeat the process: 116 / 21

Let's proceed to step 3:
21 goes into 116 5 times with a remainder of 11.
Record the quotient 5 as the next digit in the result. 
Result so far: 25.0
Subtract 105 from 116 to get 11.
Bring next digit (1) of the dividend behind the 11 and repeat the process: 111 / 21

Let's proceed to step 4:
If we divide 111 by 21, we get 5 and a remainder of 6.
Record the quotient 5 as the next digit in the result. 
Result so far: 255.0
If we take 105 away from 111, we end up with 6.
Take the next digit (5) from the dividend and append it to 6, then repeat: 65 / 21

On to step 5:
21 can be fit into 65 3 times, resulting in a remainder of 2.
The next digit of our result is 3. 
Result so far: 2553.0
Subtract 63 from 65 to get 2.
Take the next digit (1) from the dividend and append it to 2, then repeat: 21 / 21

Advancing to step 6:
When dividing 21 by 21, we get 1 with a remainder of 0.
Write down 1 as next digit of the result. 
Result so far: 25531.0
The remainder is 0 after subtracting 21 from 21.
Include the next digit (5) from the dividend after 0, then repeat: 5 / 21

Moving on to step 7:
The number 21 fits into 5 0 times, leaving a remainder of 5.
Write down 0 as next digit of the result. 
Result so far: 255310.0
Deduct 0 from 5 and we're left with 5.
Grab the next digit (5) from the dividend, add it to 5, then carry on: 55 / 21

Advancing to step 8:
When dividing 55 by 21, we get 2 with a remainder of 13.
Write down 2 as next digit of the result. 
Result so far: 2553102.0
Subtracting 42 from 55 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.

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: 2553102.6
Subtracting 126 from 130 leaves us with 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:
When dividing 40 by 21, we get 1 with a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 2553102.61
Deduct 21 from 40 and we're left 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.

Going ahead to step 11:
190 divided by 21 is 9 with a remainder of 1.
The number 9 becomes the next digit in our result. 
Result so far: 2553102.619
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:
10 divided by 21 is 0 with a remainder of 10.
The next digit of our result is 0. 
Result so far: 2553102.619
Subtracting 0 from 10 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.

Moving on to step 13:
21 goes into 100 4 times with a remainder of 16.
The number 4 becomes the next digit in our result. 
Result so far: 2553102.61904
If we take 84 away from 100, we end up 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.

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: 2553102.619047
Deduct 147 from 160 and we're left 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.

Advancing to step 15:
The number 21 fits into 130 6 times, leaving a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 2553102.6190476
If we take 126 away from 130, we end up with 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 16:
When dividing 40 by 21, we get 1 with a remainder of 19.
Record the quotient 1 as the next digit in the result. 
Result so far: 2553102.61904761
The remainder is 19 after subtracting 21 from 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

In conclusion, the division gives 2553102.61904761 with a balance of 1.9e-08.