The ODD EVEN Blade Count - A True Story! ©
  Way back in the "good-old-days"
  about 80 years ago when wind for electrical 
  power first got its start as 36 volt battery powered lighting
  for OFF-GRID
  "Kansas Farm Homes" there was TWO blade designs and
  THREE blade 
  designs competing.That is where the whole argument originally
  started. 
  The proponents of THREE BLADES claimed that "3 blades behaves
  more 
  like a round wheel" So today this notion of an ODD number
  has been totally 
  perverted for PROFITEERING sake $$$
  
All propellers with 3 blades or more are behaving
  "more like a round wheel"
  anyhow! The argument that 10 blades gives any less of a "round
  wheel
  effect" than say 9 or 11 blades is pure "SALESMANSHIP"
  and bunk!
  
Take a look way back in the history books and you
  will find scores of
  writing on the ODD/EVEN subject from the 2 blade and 3 blade
  proponent
  folks. Turbines with 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 blades
  are ALL
  "behaving more like round wheels" already. More importantly
  is the
  blades are ALL the same weight!!! Ask the pilot of any 2 bladed
  helicopter, they work fine also as long as the blades are similar
  to the
  same weight each. I hope this helps stop all the confusion.
  
Point of interest: If you DO have a propeller with
  an EVEN number 
  of blades and one blade happens to break you can always keep
  it 
  working 'in-a-pinch' by removing the blade on the opposite side.
  Whalaa! It works again and the balance is perfect!
  You can't do this if your blades are in ODD numbers due to horrible
  vibration.