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Revision: 6788
at June 14, 2008 11:08 by banzaiman
Updated Code 
^1?$|^(11+?)\1+$

Revision: 6787
at June 14, 2008 11:07 by banzaiman
Updated Code 
/^1?$|^(11+?)\1+$/

Revision: 6786
at June 14, 2008 11:02 by banzaiman
Initial Code 
print "Prime" if (1 x shift) !~ /^1?$|^(11+?)\1+$/
Initial URL 









Initial Description





By the legendary abigail.  Fails to match if and only if it is matched against a prime number of 1's.  That is, '11' fails, but '1111' does not.

I once heard him talk why this works, but I forgot most of it.









Initial Title





Prime number tester









Initial Tags





regex









Initial Language





Regular Expression