The multiplier for "effective focal length" on the Nikon DSLRs is 1.5. Thus a 50 on a DSLR will seem like a 75mm. That's why you need a 14mm lens to give you the angle of view of a 21mm lens on 35mm.
Remember, the focal length of a lens never changes. A 50mm is a 50mm always. What changes with format is ANGLE OF VIEW. That's why 50mm is quite wide on medium format and very wide on large format. There's a trigonometric equation that relates field of view to format size and focal lentgh, but I don't have it handy.