--- a/prime	Sat Oct 29 21:59:16 2011 +0200
+++ b/prime	Sat Oct 29 22:07:12 2011 +0200
@@ -9,11 +9,14 @@
 
 my $ME = basename $0;
 
-die "$ME: Sorry, need the number\n"
+die "Usage: $ME {number}\n"
   if not @ARGV;
 
 my $number = $ARGV[0];
 
+die "$ME: Sorry, number >= 2 expected!\n"
+  if $number < 2;
+
 #1. find all divisors of $number
 my @divisors = findDivisors($number);
 print "Die Teiler von $number sind: @divisors\n";