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 A181447 Numbers n such that 3 is the largest prime factor of n^2 - 1. 29
 2, 5, 7, 17 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Sequence is finite and complete, for proof see A175607. Search for terms can be restricted to the range from 2 to A175607(2) = 17; primepi(3) = 2. LINKS MATHEMATICA Select[Range[20], FactorInteger[#^2-1][[-1, 1]]==3&] PROG (MAGMA) [ n: n in [2..20] | m eq 3 where m is D[#D] where D is PrimeDivisors(n^2-1) ]; // Klaus Brockhaus, Feb 17 2011 (PARI) is(n)=n=n^2-1; my(o=valuation(n, 3)); o && n>>valuation(n/3^o, 2)==1 \\ Charles R Greathouse IV, Jul 01 2013 CROSSREFS Cf. A175607, A181448-A181470, A181568. Sequence in context: A322440 A067580 A325210 * A082088 A075881 A208241 Adjacent sequences:  A181444 A181445 A181446 * A181448 A181449 A181450 KEYWORD nonn,fini,full AUTHOR Artur Jasinski, Oct 21 2010 STATUS approved

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Last modified October 15 05:43 EDT 2019. Contains 328026 sequences. (Running on oeis4.)