according to Vigier & Pina the N on its own indicates pre 1970 for this designer (if post 1970 there would be the addition of the L), and apparently there are a large variety of code sequences for this factory, depending on the type of glass structure.
According to Ivo's book 'Glass fact file a-z' (Millers), Orrefors 'production glass' used sequential numbering from 1935 to 1960, with 1956 commencing with No. 3571, and 1957 commencing with No. 3618 - so if I have the group correct for your piece then it would appear to have been designed in 1956.
Of course, whether that means it was actually made in that year, we'll need someone else to confirm or otherwise.