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%I #13 Sep 08 2022 08:45:54
%S 12,14,25,27,51,53,64,79,129,131,155,181,209,274,287,337,391,649,701,
%T 703,727,846,1249,1351,1457,1574,2001,3431,4159,8191,8449,13311,21295,
%U 246401
%N Numbers n such that 13 is the largest prime factor of n^2 - 1.
%C Sequence is finite and complete, for proof see A175607.
%C Search for terms can be restricted to the range from 2 to A175607(6) = 246401; primepi(13) = 6.
%t Select[Range[250000], FactorInteger[#^2-1][[-1, 1]]==13&]
%o (Magma) [ n: n in [2..250000] | m eq 13 where m is D[#D] where D is PrimeDivisors(n^2-1) ]; // _Klaus Brockhaus_, Feb 18 2011
%o (PARI) is(n)=n=n^2-1; forprime(p=2, 11, n/=p^valuation(n, p)); n>1 && 13^valuation(n, 13)==n \\ _Charles R Greathouse IV_, Jul 01 2013
%Y Cf. A175607, A181447-A181450, A181452-A181470, A181568.
%K fini,nonn,full
%O 1,1
%A _Artur Jasinski_, Oct 21 2010
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