What's NR, what's a necronomicon and what's klaatu, barads and nikto.

I googled all these things and I can't still make any sense of your comment except that it's intentionally confusing with some popular fiction references?

"Klaatu barada nikto" is a code phrase from The Day the Earth Stood Still to stop the homicidal antagonists from killing you.

It's doubly famous because Sam Raimi recycled it in "Army of Darkness" as an incantation to dispel the curse of the Necronomicon (book of the dead, portrayed as the arch book of black magic in any number of stories), which our hapless anti-hero Ash fucks up and thus unleashes the armies of the dead on a roughly medieval and wholly unprepared world.

If you like campy horror movies, there is so much camp in Army of Darkness that there's barely any room for the horror. It is technically a sequel but it works as a standalone movie. I watched it years before I finally sat down and watched The Evil Dead.

Wasn't it also used in Ghost Busters at some point?

NR is apparently Numerical Recipes, a book. I think they mean that the constants are not well understood, like the phrase "Klaatu barada nikto" was not understood, but still had an effect.

In addition to what the other answers have said, the Necronomicon is the book of dark magic in the Lovecraft mythos, from which it has been copied into some other mythoi.

It's common hacker news trope for someone to do acronym diarrhea, even with rarely or never used abbreviations. It's quite annoying.

NR is in the answer in the link.

I feel like SE being stack exchange is pretty clear here.

The remaining reference is not an acronym or abbreviation, nor do I think it looks like one.

I assume Numerical Recipes.