CodeIgniter 3.1 customized pagination lib : Display pagination by step of ten or hundred. Customisable. Optimized for big pagination and to help SEO robots to crawl your site faster. Code modification line 250 to 275. You can see a picture in comments to understand the final rendering.

MY_Pagination.php

<?php

class MY_Pagination extends CI_Pagination
{

    //Step by 10 plugin
    protected $crawl_by_ten = 0;

    //Step by 100 plugin
    protected $crawl_by_hundred = 0;

    public function __construct($config)
    {
        parent::__construct($config);
    }

    public function create_links()
  	{


  		// If our item count or per-page total is zero there is no need to continue.
  		// Note: DO NOT change the operator to === here!
  		if ($this->total_rows == 0 OR $this->per_page == 0)
  		{
  			return '';
  		}

  		// Calculate the total number of pages
  		$num_pages = (int) ceil($this->total_rows / $this->per_page);

  		// Is there only one page? Hm... nothing more to do here then.
  		if ($num_pages === 1)
  		{
  			return '';
  		}

  		// Check the user defined number of links.
  		$this->num_links = (int) $this->num_links;

  		if ($this->num_links < 0)
  		{
  			show_error('Your number of links must be a non-negative number.');
  		}

  		// Keep any existing query string items.
  		// Note: Has nothing to do with any other query string option.
  		if ($this->reuse_query_string === TRUE)
  		{
  			$get = $this->CI->input->get();

  			// Unset the control, method, old-school routing options
  			unset($get['c'], $get['m'], $get[$this->query_string_segment]);
  		}
  		else
  		{
  			$get = array();
  		}

  		// Put together our base and first URLs.
  		// Note: DO NOT append to the properties as that would break successive calls
  		$base_url = trim($this->base_url);
  		$first_url = $this->first_url;

  		$query_string = '';
  		$query_string_sep = (strpos($base_url, '?') === FALSE) ? '?' : '&amp;';

  		// Are we using query strings?
  		if ($this->page_query_string === TRUE)
  		{
  			// If a custom first_url hasn't been specified, we'll create one from
  			// the base_url, but without the page item.
  			if ($first_url === '')
  			{
  				$first_url = $base_url;

  				// If we saved any GET items earlier, make sure they're appended.
  				if ( ! empty($get))
  				{
  					$first_url .= $query_string_sep.http_build_query($get);
  				}
  			}

  			// Add the page segment to the end of the query string, where the
  			// page number will be appended.
  			$base_url .= $query_string_sep.http_build_query(array_merge($get, array($this->query_string_segment => '')));
  		}
  		else
  		{
  			// Standard segment mode.
  			// Generate our saved query string to append later after the page number.
  			if ( ! empty($get))
  			{
  				$query_string = $query_string_sep.http_build_query($get);
  				$this->suffix .= $query_string;
  			}

  			// Does the base_url have the query string in it?
  			// If we're supposed to save it, remove it so we can append it later.
  			if ($this->reuse_query_string === TRUE && ($base_query_pos = strpos($base_url, '?')) !== FALSE)
  			{
  				$base_url = substr($base_url, 0, $base_query_pos);
  			}

  			if ($first_url === '')
  			{
  				$first_url = $base_url.$query_string;
  			}

  			$base_url = rtrim($base_url, '/').'/';
  		}

  		// Determine the current page number.
  		$base_page = ($this->use_page_numbers) ? 1 : 0;

  		// Are we using query strings?
  		if ($this->page_query_string === TRUE)
  		{
  			$this->cur_page = $this->CI->input->get($this->query_string_segment);
  		}
  		elseif (empty($this->cur_page))
  		{
  			// Default to the last segment number if one hasn't been defined.
  			if ($this->uri_segment === 0)
  			{
  				$this->uri_segment = count($this->CI->uri->segment_array());
  			}

  			$this->cur_page = $this->CI->uri->segment($this->uri_segment);

  			// Remove any specified prefix/suffix from the segment.
  			if ($this->prefix !== '' OR $this->suffix !== '')
  			{
  				$this->cur_page = str_replace(array($this->prefix, $this->suffix), '', $this->cur_page);
  			}
  		}
  		else
  		{
  			$this->cur_page = (string) $this->cur_page;
  		}

  		// If something isn't quite right, back to the default base page.
  		if ( ! ctype_digit($this->cur_page) OR ($this->use_page_numbers && (int) $this->cur_page === 0))
  		{
  			$this->cur_page = $base_page;
  		}
  		else
  		{
  			// Make sure we're using integers for comparisons later.
  			$this->cur_page = (int) $this->cur_page;
  		}

  		// Is the page number beyond the result range?
  		// If so, we show the last page.
  		if ($this->use_page_numbers)
  		{
  			if ($this->cur_page > $num_pages)
  			{
  				$this->cur_page = $num_pages;
  			}
  		}
  		elseif ($this->cur_page > $this->total_rows)
  		{
  			$this->cur_page = ($num_pages - 1) * $this->per_page;
  		}

  		$uri_page_number = $this->cur_page;

  		// If we're using offset instead of page numbers, convert it
  		// to a page number, so we can generate the surrounding number links.
  		if ( ! $this->use_page_numbers)
  		{
  			$this->cur_page = (int) floor(($this->cur_page/$this->per_page) + 1);
  		}

  		// Calculate the start and end numbers. These determine
  		// which number to start and end the digit links with.
  		$start	= (($this->cur_page - $this->num_links) > 0) ? $this->cur_page - ($this->num_links - 1) : 1;
  		$end	= (($this->cur_page + $this->num_links) < $num_pages) ? $this->cur_page + $this->num_links : $num_pages;

  		// And here we go...
  		$output = '';

  		// Render the "First" link.
  		if ($this->first_link !== FALSE && $this->cur_page > ($this->num_links + 1 + ! $this->num_links))
  		{
  			// Take the general parameters, and squeeze this pagination-page attr in for JS frameworks.
  			$attributes = sprintf('%s %s="%d"', $this->_attributes, $this->data_page_attr, 1);

  			$output .= $this->first_tag_open.'<a href="'.$first_url.'"'.$attributes.$this->_attr_rel('start').'>'
  				.$this->first_link.'</a>'.$this->first_tag_close;
  		}

  		// Render the "Previous" link.
  		if ($this->prev_link !== FALSE && $this->cur_page !== 1)
  		{
  			$i = ($this->use_page_numbers) ? $uri_page_number - 1 : $uri_page_number - $this->per_page;

  			$attributes = sprintf('%s %s="%d"', $this->_attributes, $this->data_page_attr, ($this->cur_page - 1));

  			if ($i === $base_page)
  			{
  				// First page
  				$output .= $this->prev_tag_open.'<a href="'.$first_url.'"'.$attributes.$this->_attr_rel('prev').'>'
  					.$this->prev_link.'</a>'.$this->prev_tag_close;
  			}
  			else
  			{
  				$append = $this->prefix.$i.$this->suffix;
  				$output .= $this->prev_tag_open.'<a href="'.$base_url.$append.'"'.$attributes.$this->_attr_rel('prev').'>'
  					.$this->prev_link.'</a>'.$this->prev_tag_close;
  			}

  		}

  		// Render the pages
  		if ($this->display_pages !== FALSE)
  		{
  			// Write the digit links
  			for ($loop = $start - 1; $loop <= $end; $loop++)
  			{
  				$i = ($this->use_page_numbers) ? $loop : ($loop * $this->per_page) - $this->per_page;

  				$attributes = sprintf('%s %s="%d"', $this->_attributes, $this->data_page_attr, $loop);

  				if ($i >= $base_page)
  				{
  					if ($this->cur_page === $loop)
  					{
  						// Current page
  						$output .= $this->cur_tag_open.$loop.$this->cur_tag_close;
  					}
  					elseif ($i === $base_page)
  					{
  						// First page
  						$output .= $this->num_tag_open.'<a href="'.$first_url.'"'.$attributes.$this->_attr_rel('start').'>'
  							.$loop.'</a>'.$this->num_tag_close;
  					}
  					else
  					{
  						$append = $this->prefix.$i.$this->suffix;
  						$output .= $this->num_tag_open.'<a href="'.$base_url.$append.'"'.$attributes.'>'
  							.$loop.'</a>'.$this->num_tag_close;
  					}
  				}
  			}
  		}



      //Step by 10 plugin
      if($end < $num_pages-10){
        $loop = ceil($loop/10)*10;
        for($i = 0; $i < $this->crawl_by_ten; $i++){
          $append = $this->prefix.$loop.$this->suffix;
          $output .= $this->num_tag_open.'<a href="'.$base_url.$append.'">'.$loop.'</a>'.$this->num_tag_close;
          $loop += 10;
          if($loop >= $num_pages){
            break;
          }
        }
      }


      //Step by 100 plugin
      $loop = ceil($loop/100)*100;
      if($loop < $num_pages){
        for($i = 0; $i < $this->crawl_by_hundred; $i++){
          $append = $this->prefix.$loop.$this->suffix;
          $output .= $this->num_tag_open.'<a href="'.$base_url.$append.'">'.$loop.'</a>'.$this->num_tag_close;
          $loop += 100;
          if($loop >= $num_pages){
            break;
          }
        }
      }



  		// Render the "next" link
  		if ($this->next_link !== FALSE && $this->cur_page < $num_pages)
  		{
  			$i = ($this->use_page_numbers) ? $this->cur_page + 1 : $this->cur_page * $this->per_page;

  			$attributes = sprintf('%s %s="%d"', $this->_attributes, $this->data_page_attr, $this->cur_page + 1);

  			$output .= $this->next_tag_open.'<a href="'.$base_url.$this->prefix.$i.$this->suffix.'"'.$attributes
  				.$this->_attr_rel('next').'>'.$this->next_link.'</a>'.$this->next_tag_close;
  		}

  		// Render the "Last" link
  		if ($this->last_link !== FALSE && ($this->cur_page + $this->num_links + ! $this->num_links) < $num_pages)
  		{
  			$i = ($this->use_page_numbers) ? $num_pages : ($num_pages * $this->per_page) - $this->per_page;

  			$attributes = sprintf('%s %s="%d"', $this->_attributes, $this->data_page_attr, $num_pages);

  			$output .= $this->last_tag_open.'<a href="'.$base_url.$this->prefix.$i.$this->suffix.'"'.$attributes.'>'
  				.$this->last_link.'</a>'.$this->last_tag_close;
  		}

  		// Kill double slashes. Note: Sometimes we can end up with a double slash
  		// in the penultimate link so we'll kill all double slashes.
  		$output = preg_replace('#([^:"])//+#', '\\1/', $output);

  		// Add the wrapper HTML if exists
  		return $this->full_tag_open.$output.$this->full_tag_close;
  	}
}

pagination.php

$config['crawl_by_ten'] = 5;
$config['crawl_by_hundred'] = 3;