#! perl -slw
use strict;
use constant TALLY => 'tally.bin';

our $N //= 50;
my $tally = chr(0) x (10e6 / 8 );

if( -e TALLY ) {
    open I, '<:raw', TALLY or die $!;
    my $tally = do{ local $/; <I> };
    close I;
}

sub genPartNo {{
    my $partNo = int( 1e6 + rand( 9e6 ) );
    redo if vec( $tally, $partNo, 1 );
    vec( $tally, $partNo, 1 ) = 1;
    return $partNo;
}}

print genPartNo for 1 .. $N;

open O, '>:raw', TALLY or die $!;
printf O "%s", $tally;
close O;