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Reference.org
Parity problem (sieve theory)
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<p>In <a href="/facts/Number_theory/zhoa7zrc">number theory</a>, the parity problem refers to a limitation in <a href="/facts/Sieve_theory/4P5pSHV6">sieve theory</a> that prevents sieves from giving good estimates in many kinds of <a href="/facts/Prime_number/L20FLkgn">prime</a>-counting problems. The problem was identified and named by <a href="/facts/Atle_Selberg/3JDSUN2k">Atle Selberg</a> in 1949. Beginning around 1996, <a href="/facts/John_Friedlander/aVTXUsVK">John Friedlander</a> and <a href="/facts/Henryk_Iwaniec/4yVGj3lU">Henryk Iwaniec</a> developed some parity-sensitive sieves that make the parity problem less of an obstacle. </p>