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function my_blog_number_title($titletag) {
 if( is_paged() ) {
  global $wp_query;
  $pagenum = $wp_query->query_vars['paged'];
  $new_title = $titletag.' Page '.$pagenum;
  $titletag = str_replace($titletag, $new_title ,$titletag);
  return $titletag;
 }
}
add_filter('wp_render_title_tag_filter','custom_wp_render_title_tag');