What is the "N" folder attribute on Windows?

As far as I have ever known, files could have any combination of four attributes: (R)ead-only, (A)rchive, (S)ystem and (H)idden.

I have researched and found out there is also the +I attribute (indexed). But nothing about "+N".

What is this misterious +N attribute on my Vista machine?

The I and N attributes mean the same thing (for some obscure reason, Microsoft prefers to display the same attribute as "N" in Windows Explorer and as "I" in the command line, at least in Windows Vista). This attribute applies only to folders and it means "do not index".

Let's check the propierties of a regular folder on Windows Explorer.

Notice there's a setting called "Index this folder for faster searching":

On folders containing the "N" attribute, this checkmark is not checked.

Let's change the folder's attributes adding I to it .

The Windows Explorer view reflects the new attribute:

The N stands for Not indexed.

(source)

Windows Vista not withstanding, in Windows 10, from my experimentation and experience (without going back, again, into MSDN .NET libraries and see what the FileAttributes are) here is what I have observed:

1) No attributes on an object will show a file with "N" in Windows Explorer, thus assuming this is MS's way of indicating "Normal" object (file) with indexing enabled.

2) When other attributes are on, such as +R or +A, and the object is indexed enabled, then those attributes will show, but there will be no "N".

3) When no attributes are on, but the object is NOT indexed, then Windows Explorer shows "I" attributes. IMHO, this is counter intuitive, but given what was (XP and before) to now what is (VISTA and beyond), this is how it works.

So in summary "N" is normal with no other attributes and object is indexed, "I" is NOT indexed with (or without) other attributes set.