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 A181449 #19 Dec 21 2024 14:20:34 %S A181449 6,8,13,15,29,41,55,71,97,99,127,244,251,449,4801,8749 %N A181449 Numbers k such that 7 is the largest prime factor of k^2 - 1. %C A181449 Numbers k such that A076605(k) = 7. %C A181449 Sequence is finite and complete, for proof see A175607. %C A181449 Search for terms can be restricted to the range from 2 to A175607(4) = 8749; primepi(7) = 4. %t A181449 Select[Range[9000], FactorInteger[#^2-1][[-1, 1]]==7&] %o A181449 (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 A181449 (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 A181449 Row 4 of A223701. %Y A181449 Cf. A076605, A175607, A181447, A181448, A181450-A181470, A181568. %K A181449 fini,full,nonn %O A181449 1,1 %A A181449 _Artur Jasinski_, Oct 21 2010