Googology Wiki
Googology Wiki

17 (seventeen) is a positive integer following 16 and preceding 18. Its ordinal form is written "17th" or "seventeenth".


  • 17 is odd prime number. It is the third Fermat prime \(2^{2^2}+1\).
  • 17 is the smallest number of clues that a sudoku puzzle can have.[1]
  • 17 is associated with bad luck in Italian superstition.
  • Ironically, the prize for 2 correct final digits in the German lottery Spiel 77 is equal to 17 euros.

In googology

  • In Greek-based naming systems, 17 is associated with prefix "heptadeka-", and with prefix "septendeci-" in Latin systems.
  • 17 is the 6th output of the Xi function, \(\Xi(6) = 17\).


  1. McGuire, G., Tugeman, B. and Civario, G. (2014). "There Is No 16-Clue Sudoku: Solving the Sudoku Minimum Number of Clues Problem via Hitting Set Enumeration". Exmerimental Mathematics, 23(2) pp. 190-217. doi:10.1080/10586458.2013.870056