We look at the division of 63642636 by 621 
The aim is to understand the frequency of 621 in 63642636.

Going ahead to step 1:
The number 621 fits into 6 0 times, leaving a remainder of 6.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 6, we end up with 6.
Bring next digit (3) of the dividend behind the 6 and repeat the process: 63 / 621

Step 2:
The number 621 fits into 63 0 times, leaving a remainder of 63.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtracting 0 from 63 leaves us with 63.
Append the next digit (6) from the dividend to 63 and continue with: 636 / 621

Moving on to step 3:
The number 621 fits into 636 1 times, leaving a remainder of 15.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
Deduct 621 from 636 and we're left with 15.
Take the next digit (4) from the dividend and append it to 15, then repeat: 154 / 621

Advancing to step 4:
The number 621 fits into 154 0 times, leaving a remainder of 154.
Use 0 as the next digit of our solution. 
Result so far: 10.0
Subtracting 0 from 154 leaves us with 154.
Bring next digit (2) of the dividend behind the 154 and repeat the process: 1542 / 621

Let's proceed to step 5:
621 can be fit into 1542 2 times, resulting in a remainder of 300.
Record the quotient 2 as the next digit in the result. 
Result so far: 102.0
If we take 1242 away from 1542, we end up with 300.
Grab the next digit (6) from the dividend, add it to 300, then carry on: 3006 / 621

On to step 6:
621 goes into 3006 4 times with a remainder of 522.
The number 4 becomes the next digit in our result. 
Result so far: 1024.0
The remainder is 522 after subtracting 2484 from 3006.
Grab the next digit (3) from the dividend, add it to 522, then carry on: 5223 / 621

Going ahead to step 7:
5223 divided by 621 is 8 with a remainder of 255.
The number 8 becomes the next digit in our result. 
Result so far: 10248.0
If we take 4968 away from 5223, we end up with 255.
Grab the next digit (6) from the dividend, add it to 255, then carry on: 2556 / 621

Advancing to step 8:
621 goes into 2556 4 times with a remainder of 72.
Put 4 as the next digit of the answer. 
Result so far: 102484.0
Deduct 2484 from 2556 and we're left with 72.
Since there are no more digits in the dividend, we add a zero to the remainder making it 720, and continue the process.

Going ahead to step 9:
The number 621 fits into 720 1 times, leaving a remainder of 99.
Put 1 as the next digit of the answer. 
Result so far: 102484.1
If we subtract 621 from 720, we get 99.
Since there are no more digits in the dividend, we add a zero to the remainder making it 990, and continue the process.

Moving on to step 10:
The number 621 fits into 990 1 times, leaving a remainder of 369.
Put 1 as the next digit of the answer. 
Result so far: 102484.11
Deduct 621 from 990 and we're left with 369.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3690, and continue the process.

Our division results in 102484.11 with a remaining 0.369.