how do you insert a special post in Wordpress after 7 posts?

I hav开发者_C百科e this code which inserts my side bar after 7 posts in my wordpress theme, the issue is that this code places the sidebar every 7 posts, I just want it to appear once.

 <?php $postnum++; if($postnum%7 == 0) { ?>
   <div class="post-single nolink">
      <?php get_sidebar(); ?>
          </div>  
 <?php } ?>

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You don't have to use modulus operator then. Simply use:

<?php $postnum++; if($postnum == 7) { ?>
   <div class="post-single nolink">
      <?php get_sidebar(); ?>
          </div>  
 <?php } ?>