ok.. it would help to know what was in $p and what you were trying to do. for(;;) loops aren't as commonly used in Perl as they are in C as there are often more convenient idioms.

#Assume @p is a list of numbers?
my @p=(0..10); 


for($x = $prevmax;$x<=$max;$x++){   
      $n = sqrt($x);
      $i = 0;
      #Dividing by 0 is always an error... make sure $p[$i] is true
      while ( ($p[$i]) && ($x%$p[$i] !=0) ) {
         $i++;         
         if (($n < $p[$i]) && ($x > $p[-1])) { 
            print (1 & ($x > $p[-1])); # <--what are you expecting her
+e
            push(@p,$x."\n");
            last;
         }
      }
}
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