obdurately vs pertinaciously

obdurately

adv
  • In an obdurate manner; stubbornly, intractably or inflexibly. 

pertinaciously

adv
  • In a stubbornly resolute manner; tenaciously holding one's opinion or course of action. 

How often have the words obdurately and pertinaciously occurred in a corpus of books? (source: Google Ngram Viewer )