I think You could make while factor <= n/2, since math.floor(500/(250*5)) for example will be 0 anyway

Lua:

You can cheat with the last booleans test by just returning a separate prewritten answer for this case.

(add more boolean tests or make random boolean tests?)

Now that I see everyone else's solutions, I realize I'm so beyond repair...

Lua

my answer lies in the lastdigits[i]

this passes the time limit:

print(i, lastdigits[i])
return 0 

this does not:

print(i, lastdigits[i])
return lastdigits[i]

It doesnt seem to be an optimization problem, because the code doesnt pass the time limit only when i return the table element, but I can call it anywhere else in the code for however many times and there will be no problem

Lua.

My answer is lies in an array b, so the return value is table.concat(b)

Last two lines of the code:

 print("answer = " .. table.concat(b))
  return(table.concat(b))

what I get:

Log:

answer = dmkyeCSddyGacrHsmufzNtbxrWihibkCxgdzyqpgAqdnk

and

Expected objects to be equal.
Passed in:
(string) 'dmkyeCSddyGacrHsmufzNtbxrWihibkCxgdzyqpgAqdnk'
Expected:
(string) 'dmkyeCSddyGacrHsmufzNtbxrWihibkCxgdzyqpg-aqdnk'

The answer seems to be correct, but the random test tests my answer against an incoorect value - the result string can't have dashes

same thing. all the tests work, but random test fails for some reason, as if it expects the output to be the original string

Passed in:
(string) 'jXhvjapjGxLambXinoLrbvevsmLiFtcrtoBqtoLqpmmtifg'  
Expected:
(string) 'jXhvjapjGxLambXinoLrbvevsm_liFtcrtoBqtoLqpmmtifg'

** including the SET itself, so i remove it