Drupal 7: A block that displays posts if the day it was created is a prime number

prime.module

<?php
/**
 * @file
 * A block module that displays items
*/


/**
 * Implements hook_block_info().
 */
function prime_block_info()
{
    $blocks = array();
    $blocks['prime'] = array(
    'info' => t('Prime Block'),
  );
    return $blocks;
}

/**
 * Custom content function.
 *
 * Set beginning and end dates, retrieve posts from database
 * saved in that time period.
 *
 * @return
 *   A result set of the targeted posts.
 */
function prime_posts_contents()
{
    //Get today's date if it is a prime number.
    $today = getdate();
    //Calculate the date five days ago.
    $start_time = mktime(0, 0, 0, $today['mon'], ($today['mday'] - 5), $today['year']);
    //Get all posts from five days ago to the present
    $end_time = time();
    //Use Database API to retrieve current posts.
    $query = db_select('node', 'n')
    ->fields('n', array('nid', 'title', 'created'))
    ->condition('status', 1) //Published.
    ->condition('created', array($start_time, $end_time), 'BETWEEN')
    ->orderBy('created', 'DESC') //Most recent first.
    ->execute();


    return $query;
}

//debug database fields
  function prime_query_alter($query)
  {
      if (module_exists('prime')) {
          //dpm((string) $query);
      //dpm($query->arguments());
      //dpm(entity_get_info()); //gets a list of all defined entities
      //dpm(field_info_fields()); //gets a list of all defined fields
      //dpm((string) $query);
      //dpm(entity_get_info()); //gets a list of all defined entities
      //dpm(field_info_fields()); //gets a list of all defined fields
      }
  }

/**
 * Implements hook_block_view().
 *
 * Prepares the contents of the block.
 */
function prime_block_view($delta = '')
{
    switch ($delta) {
    case 'prime':
      $block['subject'] = t('Prime posts');
      if (user_access('access content')) {
          // Use our custom function to retrieve data.
          $result = prime_posts_contents();
          // Array to contain items for the block to render.
          $items = array();
          // Iterate over the resultset and format as links.
          foreach ($result as $node) {
              $day = format_date("$node->created", 'custom', "j");

          //find days that are prime
              if ($day > 1 && (($day%2 >= 1) && ($day%3 >= 1) && ($day%5 >= 1))) {
                  $items[] = array(
                'data' => l($node->title, 'node/' . $node->nid) . " " . t('created on ' . $day)
            );

                  if (is_numeric($day)) {
                      echo "Yes, $day is numeric, ";
                  } else {
                      echo "No";
                  }
                  if ($day > 1 && (($day%2 >= 1) && ($day%3 >= 1) && ($day%5 >= 1))) {
                      echo "$day is a prime number ";
                  } else {
                      echo "$day is a not prime number";
                  }


                  if (empty($items)) {
                      $block['content'] = t('No posts available.');
                  }



                  // Pass data through theme function.
                  $block['content'] = theme(
                  'item_list',
                  array(
                'items' => $items,
                'day' => $day)
            );

                  dpm($items);
              }
          }
          return $block;
      }
}
}