Nats magic number is 48 for both the division and the wild card. Not sure which one is the big one to track, probably the division since that is the one that gets the champagne party (which was really overdone in 2012 and 2014 considering all they did was win a five team division).
Magic Numbers:
Home field NLCS - 58 (Cubs have control)
Home field NLDS - 54 (Giants)
Division - 48 (Marlins)
Home Wild Card - 49 (Cards)
Playoffs - 48 (Marlins)