recurrency vs recursion

recurrency

noun
  • The act or process of recurring; recurrence 

recursion

noun
  • The act of recurring. 

  • The act of defining an object (usually a function) in terms of that object itself. 

  • The invocation of a procedure from within itself. 

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