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 A195418 #30 Dec 26 2023 09:43:06
%S A195418 1,1,3,5,3,33,5,33,341,1045,189,1299,891,4437,9477,581,3855,105525,
%T A195418 27825,23751,173043,10531345,56511,2386125,380955,256861,24926139,
%U A195418 5108467,32397379,930343095,930291,36512775
%N A195418 a(n) = phi(C(n)) / gcd(C(n)-1, phi(C(n))), where C(n) is the n-th Cullen number.
%C A195418 When C(n) is prime (or 1), then a(n) = 1; that is, n is in A005849.
%C A195418 On the penultimate page of their paper, Grau and Luca ask for "a good (large) lower bound on this quantity which is valid for all n and which tends to infinity with n."
%H A195418 Amiram Eldar, <a href="/A195418/b195418.txt">Table of n, a(n) for n = 0..848</a>
%H A195418 José María Grau Ribas and Florian Luca, <a href="https://doi.org/10.1090/S0002-9939-2011-10899-2">Cullen numbers with the Lehmer property</a>, Proceedings of the American Mathematical Society, Vol. 140, No. 1 (2012), pp. 129-134, <a href="http://arxiv.org/abs/1103.3578">preprint</a>, arXiv:1103.3578 [math.NT], Mar 18, 2011.
%e A195418 a(2) = 3 because the second Cullen number is 9; phi(9) = 6, therefore 6/gcd(8, 6) = 6/2 = 3.
%t A195418 cullen[n_] := n(2^n) + 1; Table[EulerPhi[cullen[n]]/GCD[cullen[n] - 1, EulerPhi[cullen[n]]], {n, 0, 39}]
%o A195418 (PARI) a(n)=my(C=n<<n,p=eulerphi(C+1));p/gcd(C,p) \\ _Charles R Greathouse IV_, Feb 05 2013
%Y A195418 Cf. A000010, A002064, A005849, A160595.
%K A195418 nonn,easy
%O A195418 0,3
%A A195418 _Alonso del Arte_, Sep 20 2011