Number theory · Primes · Divisor counting · Modular arithmetic
Find every prime \(p\) for which the number \(p^2 + 11\) has fewer than \(11\) positive divisors.
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Slovenian High School Mathematics Competition for Vega Awards (MaSSA), drzavno (national) round 2005, 1. letnik, category A, problem 2. Organized by DMFA Slovenije (Society of Mathematicians, Physicists and Astronomers of Slovenia). Source