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Primes P such that P < (largest prime factor of (P-1)) * (largest prime factor of (P+1)).

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`%I #11 Oct 29 2022 10:20:28
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`%S 2,3,5,11,13,23,29,37,43,47,59,61,67,73,83,103,107,113,131,137,139,
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`%T 149,157,167,173,179,193,211,223,227,229,233,263,269,277,281,283,293,
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`%U 311,313,317,331,347,353,359,367,373,383,389,397,409,421,439,443,457,467
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`%N Primes P such that P < (largest prime factor of (P-1)) * (largest prime factor of (P+1)).
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`%e For n = 3, a(3)=11.
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`%e The prime P = 11
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`%e P-1 = 10 (largest prime factor of 10 is 5)
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`%e P+1 = 12 (largest prime factor of 12 is 3)
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`%e 11 < 5*3.
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`%t Select[Prime[Range[100]],#<(FactorInteger[#-1][[-1,1]] FactorInteger[#+1][[-1,1]])&] (* _Harvey P. Dale_, Feb 22 2011 *)
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`%o (PARI) isok(p) = (p==2) || (isprime(p) && (p < vecmax(factor(p-1)[, 1]) * vecmax(factor(p+1)[, 1]))); \\ _Michel Marcus_, Oct 29 2022
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`%Y Cf. A180641. See also A103666, A103667.
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`%K nonn
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`%O 1,1
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`%A _Karl Hovekamp_, Sep 14 2010
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`%E Initial term, i.e., 2, added by _Harvey P. Dale_, Feb 22 2011
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