This is a fun formula that caught my eye a while ago in HN, it looks flashy and very cool. Of course, just like others do their estimations, this one is just a made up formula and without any formal validity, apart from supposedly personal experience:

https://news.ycombinator.com/item?id=37965582

  My estimate math:
  
  R = t × [1.1^ln(n+p) + 1.3^X]
  
  R - time it really takes.
  
  t - shortest possible time it would take without need to communicate.
  
  n - number of people working and involved during the process, both customers and developing organization.
  
  p - longest communication distance network involved in the project (typically from the lowest level developer to the end user)
  
  X - number of new tools, libraries, techniques, used in the process.
  
  Example. Project involving one developing writing code. Project would take 2 weeks (t=2), but it has 5 people (n=5) involved total, only 1 new tool (X=1) and longest communication distance is 4.
  
  2×(1.1^ln(5+4) + 1.3^1) = 4.5 weeks.

The X factor is likely correct, but needs some additional notes.

Include additional X quantity for unknown unknowns, not just the known unknowns.