%I #13 Sep 08 2022 08:45:54

%S 10,21,23,34,43,65,76,89,109,111,197,199,241,351,485,769,881,1079,

%T 6049,19601

%N Numbers n such that 11 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(5) = 19601; primepi(11) = 5.

%t Select[Range[20000], FactorInteger[#^2-1][[-1, 1]]==11&]

%o (Magma) [ n: n in [2..20000] | m eq 11 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, 7, n/=p^valuation(n, p)); n>1 && 11^valuation(n, 11)==n \\ _Charles R Greathouse IV_, Jul 01 2013

%Y Cf. A175607, A181447-A181449, A181451-A181470, A181568.

%K fini,full,nonn

%O 1,1

%A _Artur Jasinski_, Oct 21 2010