Post Type: "Attachment and Post" / slug issue (page1, page2,,)

Hi,

I input “page1” into the slug of Attachment and I publish it,
and then, I go to the attachment page,
but that page redirects me to the parent post.

“page2”, “page3”, …. “page(n)” also.

I check other post type, and

As for “Post”, “page(n)” is not available for slug, too.
But as for “Page”, if i try to use “page(n)”, WordPress makes it change “page(n)-(n)”.

Thanks.