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 A344456 #21 Feb 07 2022 14:01:52
%S A344456 41124,230867,358267,37539572,148025049,235167249,242788284,
%T A344456 1085464188,142772845653,202728626748
%N A344456 Composite numbers k such that (k-1) divides (A018804(k)-1).
%C A344456 For any prime p, (p-1) divides (A018804(p)-1) = 2(p-1).
%C A344456 Some larger terms: 62763888399737.
%H A344456 Pruthviraj et al., <a href="https://mathoverflow.net/q/393216">Are there infinitely many composite a such that Sum_{k=1..a} (k,a) == 1 (mod a-1)?</a>, MathOverflow, 2021.
%t A344456 f[p_, e_] := (e*(p - 1)/p + 1)*p^e; pil[n_] := Times @@ f @@@ FactorInteger[n]; Select[Range[2, 400000], CompositeQ[#] && Divisible[pil[#] - 1, # - 1] &] (* _Amiram Eldar_, May 19 2021 *)
%Y A344456 Cf. A018804.
%K A344456 nonn,hard,more
%O A344456 1,1
%A A344456 _Max Alekseyev_, May 19 2021
%E A344456 a(9)-a(10) confirmed by _Martin Ehrenstein_, May 27 2021