Find the sum of all prime numbers between zero and two million and encode the answer

output.txt

$  php -f sum_primes.php
Sum: 142913828922

Sum to Hex:
31 34 32 39 31 33 38 32 38 39 32 32

Hex to Base64:
MzEgMzQgMzIgMzkgMzEgMzMgMzggMzIgMzggMzkgMzIgMzIg
$

sum_primes.php

<?php

/**
 * @File
 * Calculate the sum of all primes from 0-2000000.
 * 
 * Special thanks to my reddit secret santa!
 */

// Cheat by downloading a list of pre-generated primes.
$filename = 'primes1.zip';
if (!file_exists($filename)) {
  $primes_zip = file_get_contents('http://primes.utm.edu/lists/small/millions/primes1.zip');
  file_put_contents($filename, $primes_zip);
}

$primes_data = file_get_contents('zip://' . $filename . '#primes1.txt');

$primes = [];
preg_match_all('/\s(\d+)\s/', $primes_data, $primes);

// Add!
$sum = 0;
$prime = 0;
foreach ($primes[1] as $prime) {
  // Stop at 2000000
  if ($prime > 2000000) {
    break;
  }

  $sum += $prime;
}

echo 'Sum: ' . $sum . PHP_EOL . PHP_EOL;

// Convert the answer to Hex
$answer_hex = '';
foreach (str_split($sum) as $char) {
  $dec = ord($char);
  $hex = dechex($dec);
  $answer_hex .= str_pad($hex, 2, 0, STR_PAD_LEFT) . ' ';
}

echo 'Sum to Hex: ' . PHP_EOL . $answer_hex . PHP_EOL . PHP_EOL;
echo 'Hex to Base64: ' . PHP_EOL . base64_encode($answer_hex) . PHP_EOL;