Or more likely they are just skipping the number 4 which sounds like death in Chinese and Japanese, and is considered unlucky (like 13 in some western cultures). Most Japanese manufacturers skip number 4 in model sequences:
Eg. Panasonic GF1,2,3,5,6,7. LX1,2,3,5,7, Sony NEX 3,5,6,7. Olympus EPL1,2,3,5,6,7 …etc …etc
Hands-on with Nikon’s new D5500
Posted by Chris Roubis on 6th, Jan, 2015
Source Article from http://www.dpreview.com/articles/5296953047/hands-on-with-nikons-new-d5500
Started out doing photography at the age of 6 using an uncle's old 1940 kodak brownie box camera. At 15 years of age, I decided to buy my very own 1975 Praktica SLR camera. I now shoot with a Nikon D850. I do unpaid TFP and commercial paid work.