use warnings;
use strict;
use Acme::Tools qw(minus);
use List::Util  qw(shuffle);

my @alls    = 0 .. 9;
my @useds   = qw(1 2 5 8); # from your aj.db
my @unuseds = shuffle(minus(\@alls, \@useds));
my $new_num = $unuseds[0];