15405777 ÷ 644 
The aim is to understand the frequency of 644 in 15405777.

Step 1:
1 divided by 644 is 0 with a remainder of 1.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtracting 0 from 1 leaves us with 1.
Take the next digit (5) from the dividend and append it to 1, then repeat: 15 / 644

Advancing to step 2:
When dividing 15 by 644, we get 0 with a remainder of 15.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 15, we end up with 15.
Include the next digit (4) from the dividend after 15, then repeat: 154 / 644

Step 3:
The number 644 fits into 154 0 times, leaving a remainder of 154.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 154 to get 154.
Include the next digit (0) from the dividend after 154, then repeat: 1540 / 644

Let's proceed to step 4:
644 can be fit into 1540 2 times, resulting in a remainder of 252.
Put 2 as the next digit of the answer. 
Result so far: 2.0
If we take 1288 away from 1540, we end up with 252.
Bring next digit (5) of the dividend behind the 252 and repeat the process: 2525 / 644

Moving on to step 5:
If we divide 2525 by 644, we get 3 and a remainder of 593.
Use 3 as the next digit of our solution. 
Result so far: 23.0
If we subtract 1932 from 2525, we get 593.
Append the next digit (7) from the dividend to 593 and continue with: 5937 / 644

Step 6:
644 can be fit into 5937 9 times, resulting in a remainder of 141.
The number 9 becomes the next digit in our result. 
Result so far: 239.0
Subtract 5796 from 5937 to get 141.
Append the next digit (7) from the dividend to 141 and continue with: 1417 / 644

On to step 7:
644 goes into 1417 2 times with a remainder of 129.
Write down 2 as next digit of the result. 
Result so far: 2392.0
The remainder is 129 after subtracting 1288 from 1417.
Take the next digit (7) from the dividend and append it to 129, then repeat: 1297 / 644

Advancing to step 8:
644 can be fit into 1297 2 times, resulting in a remainder of 9.
The next digit of our result is 2. 
Result so far: 23922.0
The remainder is 9 after subtracting 1288 from 1297.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

On to step 9:
When dividing 90 by 644, we get 0 with a remainder of 90.
Write down 0 as next digit of the result. 
Result so far: 23922.0
Subtracting 0 from 90 leaves us with 90.
Since there are no more digits in the dividend, we add a zero to the remainder making it 900, and continue the process.

On to step 10:
The number 644 fits into 900 1 times, leaving a remainder of 256.
Record the quotient 1 as the next digit in the result. 
Result so far: 23922.01
Deduct 644 from 900 and we're left with 256.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2560, and continue the process.

On to step 11:
2560 divided by 644 is 3 with a remainder of 628.
Record the quotient 3 as the next digit in the result. 
Result so far: 23922.013
Deduct 1932 from 2560 and we're left with 628.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6280, and continue the process.

Advancing to step 12:
644 can be fit into 6280 9 times, resulting in a remainder of 484.
Put 9 as the next digit of the answer. 
Result so far: 23922.0139
If we subtract 5796 from 6280, we get 484.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4840, and continue the process.

Advancing to step 13:
When dividing 4840 by 644, we get 7 with a remainder of 332.
Use 7 as the next digit of our solution. 
Result so far: 23922.01397
If we take 4508 away from 4840, we end up with 332.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3320, and continue the process.

Let's proceed to step 14:
644 can be fit into 3320 5 times, resulting in a remainder of 100.
Put 5 as the next digit of the answer. 
Result so far: 23922.013975
If we subtract 3220 from 3320, we get 100.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1000, and continue the process.

Going ahead to step 15:
644 goes into 1000 1 times with a remainder of 356.
The next digit of our result is 1. 
Result so far: 23922.0139751
Subtracting 644 from 1000 leaves us with 356.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3560, and continue the process.

Going ahead to step 16:
644 goes into 3560 5 times with a remainder of 340.
Record the quotient 5 as the next digit in the result. 
Result so far: 23922.01397515
The remainder is 340 after subtracting 3220 from 3560.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3400, and continue the process.

After the division, we end up with 23922.01397515 and a remainder of 3.4e-07.