Polymath5 was devoted to the Erdős discrepancy problem. It ran in 2010 and there were a few additional posts in 2012, without reaching a solution. The problem has now been solved by Terry Tao using some observations from the polymath project combined with important recent developments in analytic number theory. See this blog post from Tao’s blog and this concluding blog post from Gowers’s blog.
September 22, 2015
The Erdős discrepancy problem has been solved by Terence Tao
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