There is a little disagreement on the internet as to whether this quote is due to the Hungarian mathematician Paul Erdös or the Danish mathematician Piet Hein - most primary sources agree that it is Hein, which is what I am going with (I admit that I first pulled my information off of the internet). By initially attributing the quote to Erdös I was inadvertently helping to propagate the confusion! This page was created as a partial penance for that. My mistake was first pointed out to me in September 2007 by my friend Greg Huber.
Apparently Hein produced many of these small poems, which he called Grooks. I am not sure where I drew my original information, but a little time with Google will show you that there are many secondary sources attributing this quote to Erdös. Both seemed to delight in playing with words.
|  Piet Hein (1905-1996)  |
|  Paul Erdös (1913-1996)  |