How many Ahriman/Mephiston level Librarians to take out a single Primarch?

[Tyzuris]

So basically how many Ahriman/Mephiston level Librarians would be generally needed to take out a single Primarch that is not gifted in the use of Psyker arts such as Ferrus Manus, Angron, Fulgrim or Perturabo?

Like assuming the fight took place let's say in a metropolitan environment where the Primarch starts a few tens of kilometers away from the Librarian force.

 

[LindyAF]

This is a bit like asking "how many artillery pieces would be needed to take out General Patton?" but IMO a hundred or so should do the trick in most cases well within safety margins.

 

[The Whispering Monk]

This assumes that your Brotherhood of Psykers is sufficiently aware of the Primarch and are able to actually prevent him from thinning their herd.

 

[Crazysaneman]

One if he's careful enough.

 

[Emperor Tippy]

Anywhere from one to all of them, depending entirely on what the author feels like doing.