Rather than executing thousands of queries to test each ID individually, get all ids then just test for each potential ID in the results.

my $results = $dbh->selectall_arrayref("SELECT ID from table", { Slice
+ => {} });

my %ids = map { $_->{ID}  => '1' } @$results;

for ( 1 .. 10000 )
{
        next if $ids{$_};
        #do site stuff here or push to an array to use later
        print "$_\n";
}
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