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 A181451 #17 Dec 21 2024 15:20:42 %S A181451 12,14,25,27,51,53,64,79,129,131,155,181,209,274,287,337,391,649,701, %T A181451 703,727,846,1249,1351,1457,1574,2001,3431,4159,8191,8449,13311,21295, %U A181451 246401 %N A181451 Numbers k such that 13 is the largest prime factor of k^2 - 1. %C A181451 Numbers k such that A076605(k) = 13. %C A181451 Sequence is finite and complete, for proof see A175607. %C A181451 Search for terms can be restricted to the range from 2 to A175607(6) = 246401; primepi(13) = 6. %t A181451 Select[Range[250000], FactorInteger[#^2-1][[-1, 1]]==13&] %o A181451 (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 A181451 (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 A181451 Row 6 of A223701. %Y A181451 Cf. A076605, A175607, A181447-A181450, A181452-A181470, A181568. %K A181451 fini,nonn,full %O A181451 1,1 %A A181451 _Artur Jasinski_, Oct 21 2010