This article is from the rec.arts.sf.written FAQ, by Evelyn C. Leeper evelynleeper@geocities.com with numerous contributions by others.
Traditionally, the answer has been Fredric Brown's "Knock": "The last
man on earth sat alone in a room. There was a knock on the door...."
This appeared in the december 1948 issue of THRILLING WONDER STORIES.
But there is a reference in an article by Anthony Burgess that cited,
"That morning the sun rose in the west." However, I suspect he just
composed that himself, and never published it as a separate story.
("Anthony Burgess on the Short Story," in Les Cahiers de la nouvelle
"Journal of the Short Story in English, janvier 1984, pp. 31-47.
Universite d'Angers,
http://buweb.univ-angers.fr/EXTRANET/AnthonyBURGESS/ShortStory.html.)
And Forry Ackerman claims he wrote the shortest one ever, titled
"Cosmic Report Card: Earth" consisting of the single letter "F". (In
the United States, grading is by letter: A, B, C, D, and F. Don't ask
me why E is skipped, though Jeremy Meyers suggests it is because it
would be too easy for students to alter an "F" to look like an "E".)
See http://www.jophan.org/mimosa/m16/16_p05.html for details; it
appeared in the June 1973 issue of VERTEX.)
[Provided by Evelyn Leeper [evelynleeper@geocities.com].
Updates/corrections welcome.]
 
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