|
%I #15 Sep 08 2022 08:45:54
%S 6,8,13,15,29,41,55,71,97,99,127,244,251,449,4801,8749
%N Numbers n such that 7 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(4) = 8749; primepi(7) = 4.
%t Select[Range[9000], FactorInteger[#^2-1][[-1, 1]]==7&]
%o (Magma) [ n: n in [2..9000] | m eq 7 where m is D[#D] where D is PrimeDivisors(n^2-1) ]; // _Klaus Brockhaus_, Feb 17 2011
%o (PARI) is(n)=n=n^2-1; forprime(p=2, 5, n/=p^valuation(n, p)); n>1 && 7^valuation(n, 7)==n \\ _Charles R Greathouse IV_, Jul 01 2013
%Y Cf. A175607, A181447, A181448, A181450-A181470, A181568.
%K fini,full,nonn
%O 1,1
%A _Artur Jasinski_, Oct 21 2010
|
