This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A181448 #20 Dec 21 2024 14:19:38 %S A181448 4,9,11,19,26,31,49,161 %N A181448 Numbers k such that 5 is the largest prime factor of k^2 - 1. %C A181448 Numbers k such that A076605(k) = 3. %C A181448 Sequence is finite and complete, for proof see A175607. %C A181448 Search for terms can be restricted to the range from 2 to A175607(3) = 161; primepi(5) = 3. %t A181448 Select[Range[200], FactorInteger[#^2-1][[-1, 1]]==5&] %o A181448 (Magma) [ n: n in [2..200] | m eq 5 where m is D[#D] where D is PrimeDivisors(n^2-1) ]; // _Klaus Brockhaus_, Feb 17 2011 %o A181448 (PARI) is(n)=n=n^2-1; n>>=valuation(n,2); n/=3^valuation(n,3); n>1 && 5^valuation(n, 5)==n \\ _Charles R Greathouse IV_, Jul 01 2013 %Y A181448 Row 3 of A223701. %Y A181448 Cf. A076605, A175607, A181447, A181449-A181470, A181568. %K A181448 fini,full,nonn %O A181448 1,1 %A A181448 _Artur Jasinski_, Oct 21 2010