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 A250405 #34 Apr 18 2025 21:12:21
%S A250405 1,3,15,255,65535,4294967295
%N A250405 Numbers k such that all values of Euler phi (A000010) of all divisors of k are pairwise distinct and represent all proper divisors of k+1.
%C A250405 Numbers k such that {phi(d) : d|k} = {d : d|(k+1), d<(k+1)} as multisets.
%C A250405 Conjecture: last term is 4294967295.
%C A250405 First six terms coincide with A051179. - _Omar E. Pol_, Apr 12 2025
%e A250405 15 is in the sequence because {phi(d) : d|15} = {1, 2, 4, 8} = {d : d|16, d<16}.
%e A250405 2 is not in the sequence because {phi(d) : d|2} = {1, 1}, but {d : d|2, d<2} = {1}.
%o A250405 (Magma) [n: n in [1..100000] | ([EulerPhi(d): d in Divisors(n)]) eq ([d: d in Divisors(n+1) | d lt n+1 ])];
%Y A250405 Subsequence of A250404 and A203966.
%Y A250405 Sequence differs from A051179, A050474 and A116518.
%Y A250405 Cf. A000010.
%K A250405 nonn,more,hard
%O A250405 1,2
%A A250405 _Jaroslav Krizek_, Nov 22 2014
%E A250405 Edited and a(6) added by _Max Alekseyev_, May 04 2024