No need to reformat, just use the script below to put the large primes file in a DBD::SQLite2 database. First, download and unzip the files that contain the first 15 million primes in chunks of 1 million. You will have primes1.txt through primes15.txt in a directory. Run this there:

#!/bin/perl
use strict; use warnings;

use DBI;
my $dbh = DBI->connect('dbi:SQLite2:dbname=primes.db','','',{RaiseErro
+r=>1});
my $cnt = 0;

# 'number' has to be text because of length
$dbh->do('CREATE TABLE primes (id INTEGER, number TEXT)');

for (1..15) { $cnt = add_primes($dbh,$cnt,"primes$_.txt") }

sub add_primes {
    my ($db, $c, $filename) = @_;

    open my $file, '<', $filename or die("Can't read '$filename': $!")
+;
    print STDERR "Adding primes from $filename\n";
    
    #first two lines are not data, skip them
    for (1..2) { <$file> }

    eval {
        $db->begin_work;
        my $sth = $db->prepare('INSERT INTO primes (id,number) VALUES 
+(?,?)');
        while (<$file>) {
            foreach ( split(/\s+/,$_) ) { $sth->execute(++$cnt,$_) }
        }
        $db->commit;
    };
    if ($@) {
        print STDERR "Died while processing prime #$cnt, with error:\n
+$@";
        exit;
    }

    return $cnt;
}
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Then you can always ask for the n'th prime with the SQL (? is n)

SELECT number FROM primes WHERE id = ?
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