Initial offset of number of posts in home page on the posts page

One way might be to set posts_per_page for the query to 13 and then override the $paged global (before the query is called) to force it to 2 if it is only 1… eg.

if ( (is_post_type_archive('post')) {
     global $paged;
     if ( ($paged == 0) || ($paged == 1) ) {$paged = 2;}
}