HTML code in Custom field

I’m using a custom field to display images in a slider on each post, but when I update the post after having entered the HTML code in the custom field, the code disappears. I’m assuming that there is some kind of filter that removes HTML code from custom fields when a post is saved. Is there a way to circumvent that without using a plugin?

Post X of Y in single.php / sidebar.php

Is there a way of putting “Post X of Y” into my sidebar? I think I can only show it when it is a single blog post (something like checking if the content is_single) but I want to be able to see which post I am viewing. Googling “wordpress post x of y” for the last 20 minutes has given me a lot about category x in page y or something similar, so I thought to ask here.