Modified index.php for custom sidebar widget

<?php get_header(); ?>

<section class="content">

    <?php get_template_part('inc/page-title'); ?>

    <div class="pad group">

        <?php get_template_part('inc/featured'); ?>

        <?php if ( have_posts() ) : ?>

            <div class="post-list group">

                <?php $i = 1;                       // initialize the post counter
                echo '<div class="post-row">';      // create the post-row div
                while ( have_posts() ): the_post(); ?>      <!-- while we have posts -->
                    <?php get_template_part('content'); ?>      <!-- display the post content -->

                    <?php if ($i % 2 == 0) {        // if we've shown 2 posts
                        echo '</div>';              // close this post-row div

                        // BEGIN insert my custom widget
                        if ($i % 6 == 0) {      // if we've shown 6 posts
                                    dynamic_sidebar('adsense'); // display the custom sidebar widget
                        }
                        // END insert my custom widget

                        echo '<div class="post-row">';      // create the next post-row div
                    }

                    $i++;       // increment the post counter
                    endwhile;
                    echo '</div>';      // close the post-row div
                    ?>

            </div>  <!--/.post-list-->
            <?php get_template_part('inc/pagination'); ?>

        <?php endif; ?>

    </div><!--/.pad-->

</section><!--/.content-->

<?php get_sidebar(); ?>

<?php get_footer(); ?>