windows - Batch Program - Prime Number Checker -

i'm programming in batch using fact forall n between 1 , 100, (2^n-2) mod n 0 if n prime, , not 0 if otherwise. when run program, "missing operator" error. flaw in code?

@echo off color f0 title prime number checker echo -------------------------------------------------------- echo  prime number checker v1.0 echo -------------------------------------------------------- echo. set /p n=enter number between 1 , 100:  set result=1 set i=1 :multiply set /a result=result*2 set /a i=i+1 if %i% lss %n% goto multiply set /a result = result - 2 set /a result = result % n if %result% == 0 echo number prime. if %result% neq 0 echo number not prime. pause <nul