Genesis: Add the Featured Image to Single Post pages

theme-setup.php

<?php

// Add featured image on single post
add_action( 'genesis_entry_header', 'hellopro_featured_image', 1 );
function hellopro_featured_image() {
	$image = genesis_get_image( array(
			'format'  => 'html',
			'size'    => 'featured',
			'context' => '',
			'attr'    => array ( 'class' => 'aligncenter' ),
		) );

	if ( is_singular()) {
		if ( $image ) {
			printf( '<div class="featured-image">%s</div>', $image );
		}
	}
}