with those values, they could be in a variety of projected coordinate systems.
they certainly aren't in a geographic coordinate system and they certainly aren't in UTM zone 16N, unless you are 540 km from the equator...by chance did you drop a 0 in 540000 (ie should it be 5,400,000 and not 540,000). If you dropped a zero, then it could be in utm zone 16 BUT the question now becomes, are your units in feet or meters?