The_sieve_of_Sundaram

#!/usr/local/bin/perl
#u# http://rosettacode.org/wiki/The_sieve_of_Sundaram
#c# 2021-09-04 >RC
#p# OK

use strict;
use warnings;
use feature 'say';

my @sieve;
my $nth = 1_000_000;
my $k = 2.4 * $nth * log($nth) / 2;

$sieve[$k] = 0;
for my $i (1 .. $k) {
    my $j = $i;
    while ((my $l = $i + $j + 2 * $i * $j) < $k) {
        $sieve[$l] = 1;
        $j++
    }
}

$sieve[0] = 1;
my @S = (grep { $_ } map { ! $sieve[$_] and 1+$_*2 } 0..@sieve)[0..99];
my $result = "First 100 Sundaram primes:\n" .
    (sprintf "@{['%5d' x 100]}", @S) =~ s/(.{50})/$1\n/gr;


my ($count, $index);
for (@sieve) {
    $count += !$_;
    ($result .= "\nOne millionth: " . (1+2*$index)) and last if $count == $nth;
    ++$index;
}

say $result;

my $ref = <<'END';
First 100 Sundaram primes:
    3    5    7   11   13   17   19   23   29   31
   37   41   43   47   53   59   61   67   71   73
   79   83   89   97  101  103  107  109  113  127
  131  137  139  149  151  157  163  167  173  179
  181  191  193  197  199  211  223  227  229  233
  239  241  251  257  263  269  271  277  281  283
  293  307  311  313  317  331  337  347  349  353
  359  367  373  379  383  389  397  401  409  419
  421  431  433  439  443  449  457  461  463  467
  479  487  491  499  503  509  521  523  541  547

One millionth: 15485867
END

use Test::More;
chomp $ref;
is($result, $ref);
done_testing;