MathDB
Russia 2002

Source: nice

August 25, 2007
modular arithmeticarithmetic sequencealgebra unsolvedalgebra

Problem Statement

What is the largest possible length of an arithmetic progression of positive integers a1,a2,⋯ ,an a_{1}, a_{2},\cdots , a_{n} with difference 2 2, such that {a_{k}}^{2}\plus{}1 is prime for k \equal{} 1, 2, . . . , n?
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