sub make_primes_ambrus {
    my $count=shift;
    my @primes=(2);
    my( $n, $p, $sqrp);
    NLOOP:
    for ($n=3; @primes<$count; $n+=2) {
        $sqrp = sqrt($n) + 0.5;
        for $p (@primes) {
                $sqrp < $p and last;
                0 == $n % $p and next NLOOP;
        }
        push @primes, $n
    }
    return \@primes;
}

sub make_primes_knuth  {
    my $count=shift;
    my @primes=(2);
    my $n=3;
    PRIME:
    while (@primes<$count) {
        push @primes,$n;
        while ( $n+=2 ) {
            for my $p (@primes) {
                my $r=$n % $p;
                last if !$r;
                # According to Knuth the proof of the vaildity 
                # of the following test "is interesting and a little 
                # unusual".
                next PRIME if int($n/$p) <= $p;
            }
        }
    }
    return \@primes;
}