TITLE: famous papers/results by non professional mathematicians
QUESTION [8 upvotes]: Possible Duplicate:
What recent discoveries have amateur mathematicians made? 

Dear overflowers
Out of curiosity: do you know any famous papers and/or results by non professional mathematicians? (I realize that 'non professional mathematicians' is quite vague, so let's also say 'amateur'?)
Thank you for your answers!
Edit: I meant of course math papers. Also, I am interested in somewhat recent examples, say the last 2 centuries.

REPLY [4 votes]: Robert Ammann (from Wikipedia):

Robert Ammann [...] was an amateur mathematician who made several significant and groundbreaking contributions to the theory of quasicrystals and aperiodic tilings.
Ammann attended Brandeis University, but generally did not go to classes, and left after three years. He worked as a programmer for Honeywell. After ten years, his position was eliminated as part of a routine cutback, and Ammann ended up working as a mail sorter for a post office.
He discovered several new aperiodic tilings, each among the simplest known examples of aperiodic sets of tiles. He also showed how to generate tilings using lines in the plane as guides for lines marked on the tiles, now called "Ammann bars".
Ammann's discoveries came to notice only after Penrose had published his own discovery and gained priority.

He published one paper with Grünbaum and Shephard.

REPLY [3 votes]: Kurt Heegner is a nice example. Sadly he died before the mathematical community realized that 
his proof of the class number 1 problem was essentially correct.