least vs number one

least

noun
  • Something of the smallest possible extent; an indivisible unit. 

adv
  • Used for forming superlatives of adjectives, especially those that do not form the superlative by adding -est. 

  • In the smallest or lowest degree; in a degree below all others. 

det
  • The most little; the smallest amount or quantity of something. 

prep
  • At least. 

  • What a stupid white privileged POS I am! Least I call myself out. 

  • 2019 December, Justin Blackburn, The Bisexual Christian Suburban Failure Enlightening Bipolar Blues, page 79 

number one

noun
  • Used other than figuratively or idiomatically: see number, one. 

  • The main goalkeeper of a team, so-called because they wear the number 1 on the back of their kit. 

  • The most important person, the one who is in charge. 

  • Urine; urination. 

  • A large town where theatrical performances may expect to achieve success. 

  • Oneself, being considered foremost, as by an egoist. 

  • Someone who is top of a ranking, who is ranked first. 

  • The batsman who opens the batting. 

  • The single that has sold the most in a given period. 

  • A first lieutenant. 

adj
  • First; foremost; best, often used after its headword. 

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