N-A*int(N/A) will work.  Where N mod A = 0.  (Note that this is just the remainder of N/A)

How about not(fPart(N/A)) ? It simply does the division itself, and if there is a decimal, it returns false, otherwise true.
  I think you guys are overthinking it

It returns a 0 if the argument is not an integer, 1 if it is.

fPart will return the decimal of any number, and not() will turn any non-zero number into 0, and vica versa, so if there is a decimal, the fpart extracts that, and the Not() inverts it

If fPart(A/2)
// CODE
End
This will return 1 if divisible and 0 if not divisible, according to what I got

if you have a calc with 2.53 or higher, you can use the function remainder( like this:
If not(Remainder(N,A
Then
//code
End
Remainder gives the what is left after dividing so you can also use it like this:
Remainder(N,A->X
If X=Y
bla bla bla...
remainder can be found in the math menu

but i wouldn't recommend it since it doesn't work on  OS 2.43 or lower...

To do Builder's version of the code it would looks something like this.

Prompt N,A
If not(fPart(N/A
Then
Disp "DIVISIBLE
Else
Disp "NOT DIVISIBLE
End
Or...

Prompt N,A
not(fPart(N/A
Disp sub("NOT DIVISIBLE",1+4Ans,13-4Ans
(Only saves five bytes but every byte counts in TI-BASIC )