Paul Erdos published over 1,500 papers during his lifetime. That's about one paper every 2 weeks during his career! Average professional mathematician publish about 2 papers a year. And... still he couldn't beat Euler in total number of pages published in mathematics :).

Fun fact from Wikipedia:

Erdős signed his name "Paul Erdos P.G.O.M." When he became 60, he added "L.D.", at 65 "A.D.", at 70 "L.D." and at 75 "C.D."

P.G.O.M. = "Poor Great Old Man"

L.D. = "Living Dead"

A.D. = "Archaeological Discovery"

L.D. = "Legally Dead"

C.D. = "Counts Dead"