(10 Jun 2015, 3:50 pm)Robert wrote Exactly. They have used fleet numbers with 3 consecutive numbers in the past (555 as an example).
The "problem" does not lie with the three consecutive numbers, rather the number '666' itself... If you believe in that sort of thing, '666' is often associated with the devil. The "problem", if you like, may be that this bus would be prone to more accidents and suchlike, as a result of the devil connotation.
My personal opinion is that I highly doubt GNE would miss out a fleet number simply because it has negative / unlucky connotations.