How do I add the page number to the page title on drupal default paginated pages?
Have you investigated the Page Title module? It, among other things, features


  Pagination Suffix: One of the things you may noticed about Drupal in terms of SEO is that whenever you go through a paged list of content, the page title never changes. Google Webmaster Tools will flag this up as a problem as you essentially have several different pages all being identified with the same page title. A new feature, introduced in Page Title 2.1, is the ability to append the page number as a suffix pattern. This means any URL which contains something like page=2 in the query string will also have an optional token pattern suffixed onto the end of it. Important: for this feature to work properly, you need to be running Token 1.12 or later.