1. PIN number a number you choose and use to gain access to various accounts
  2. baryon number a number equal to the difference between the number of baryons and the number of antibaryons in any subatomic structure; it is conserved in all types of particle interactions
  3. phone number the number is used in calling a particular telephone
  4. page number the system of numbering pages
  5. back-number someone who is no longer popular
  6. box number the number of a letter box at the post office where mail is collected
  7. encumber hold back, impede, or weigh down
  8. f number the ratio of the focal length to the diameter of a (camera) lens system
  9. magnanimous noble and generous in spirit
  10. Brinell number measure of the hardness of a material
  11. pen name an author's pseudonym
  12. number a concept of quantity involving zero and units
  13. burnt umber dark brown pigment obtained by heating umber
  14. prime number an integer that has no integral factors but itself and 1
  15. outnumber be larger in number
  16. mass number the sum of the number of neutrons and protons in an atomic nucleus
  17. Fibonacci number a number in the Fibonacci sequence
  18. real number any rational or irrational number
  19. call number a mark consisting of characters written on a book
  20. wave number the reciprocal of the wavelength of a wave