my @arr1 = qw/1 3 4 5 6/;
my @arr2 = qw/1 2 4 5 7 10/;

my %hash2;

@hash2{@arr2} = ("1") x @arr2;

for (sort {$a <=> $b} @arr1){
  print "$_\n" if (! defined $hash2{$_});
}


##</code><code>##

3
6