The "MC" in the picture indicates this is a Minolta MC/MD mount lens.
I think the seller doesn't know what they are talking about. The "⌀49mm" means the lens takes 49mm filters (the circle with the line through it is the diameter symbol).
Minolta MC/MD lenses won't fit on either Canon or Nikon cameras I'm not sure what the seller refers to by "Canon 49mm" (or by Nikon 52mm). However, if the lens is a Canon mount, it is probably a Canon FD mount (which was made obsolete by the Canon EF mount when they introduced their EOS cameras).
Assuming the lens is made for a Canon mount, it will not mount on a Nikon body without a "speedbooster" adapter. This is because the registration distance (also sometimes known as flange focal distance, such as at Wikipedia) of Minolta MC/MD mount is 43.5mm. Canon's EF/EF-SFD mount FFD is 4442.0mm, and Nikon's F-mount FFD is 46.5mm. Any adapterThis means that compared to mount the Vivitar lens to either Canon orFD body, a Nikon DSLRsbody is 4.5mm too thick. And a bayonet mount adapter will probably be add at least 5mm oreven more of depth, which would putdistance between the Vivitarbody and lens. If you mount a lens too far away from the Canon or Nikon bodysensor/film plane, you lose the ability to focus on distant subjects.
If you wanted to mount this lens to a Nikon F-mount DSLR (again, assuming this one is made for Canon mount), you'd need a so-called "speedbooster" (it's a mount adapter that has a refocusing element in it, to allow the Vivitar lens to focus to infinity when mounted further from the body than the designed FFD). For example, Fotodiox sells such an adapterFotodiox sells such an adapter for around $40$35 USD.
However, because you need to add a corrective lens element (the speedbooster) when mounted on Nikon bodies, the optical quality will likely be somewhat reduced. You can minimize this loss of optical performance by using a higher quality speedbooster. However, there are not very many options on the market for Minolta SR/MC/MDCanon FD lens to Nikon F-mount body adatpersadapters. The adapters will probably cost more than the lens.
In general, as a Nikon body owner, you will have to get used to having fewer lens choices (as far as adapting other brand lenses to Nikon) than any other mainstream market camera brand. Unfortunately, that's just part of the Nikon system experience.
Note: I originally assumed this lens was a Minolta MC/MD mount lens because of the "MC" text on the lens; as @osullic helpfully pointed out, "MC" stands for Multi-coated, meaning the lens has a multi-coat antireflective coating on at least one of the lens elements to prevent glare and lens reflections.