an vs up to

an

prep
  • In each; to or for each; per. 

noun
  • The first letter of the Georgian alphabet, ა (Mkhedruli), Ⴀ (Asomtavruli) or ⴀ (Nuskhuri). 

num
  • one 

article
  • Used before one and words with initial u, eu. 

  • Used before a vowel sound. 

  • Used before all consonants. 

  • Used before /h/ in an unstressed syllable. 

  • Used before /h/ in a stressed syllable. 

up to

prep
  • For the option or decision of. 

  • Until. 

  • Incumbent upon; the obligation of; the duty of. 

  • Considering all members of an equivalence class the same. 

  • Within the authority or jurisdiction of. 

  • Doing; involved in. 

  • As much as; no more than. 

  • Next to; near; towards; as far as. 

  • Ready for. 

  • Capable of. 

  • Willing to participate in. 

adj
  • maximum of. 

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