I had the pleasure to read these books, late 70s early 80s, now would like to read again on Kindle, unfortunately, I can not remember the author or book titles. They are dark, not the blood sucking type, called (Vampyres) The principle character has the ability to speak to/learn from the dead and through Moebius learns how to move through time/space by use of equations.
См. статью: A series of fictional books (6) Vampires, Necromancy, Moebius continuum?