immutability vs permanency

immutability

noun
  • The state or quality of being immutable; immutableness. 

  • The state of being unchangeable in the memory after creation. 

permanency

noun
  • The state or quality of permanence. 

  • A person or thing permanently in residence. 

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