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 A353868 #16 May 09 2022 12:01:22 %S A353868 1,2,3,4,6,8,9,12,14,15,16,18,20,24,27,28,30,32,35,36,40,42,45,48,52, %T A353868 54,56,60,63,64,65,70,72,75,78,80,81,84,90,96,98,100,104,105,108,112, %U A353868 117,119,120,126,128,130,135,140,144,150,156,160,162,168,175,180,182,189,190,192,195,196,200,204,208,210,216 %N A353868 Numbers k such that the Carmichael function A002322(k) divides Dedekind psi A001615(k). %C A353868 If coprime s,t are terms, then so is s*t. Also, if t is a term and prime p|t, then p*t is also a term. Squarefree terms are listed in A353869, primitive terms are listed in A353870, and their intersection forms A353871. %H A353868 user142929, <a href="https://mathoverflow.net/q/422010">A definition related to pseudoprimes and the Dedekind psi function</a>, MathOverflow, 2022. %t A353868 psi[1] = 1; psi[n_] := n * Times @@ (1 + 1/Transpose[FactorInteger[n]][[1]]); Select[Range[216], Divisible[psi[#], CarmichaelLambda[#]] &] (* _Amiram Eldar_, May 09 2022 *) %Y A353868 Cf. A002322, A001615, A353869, A353870, A353871. %K A353868 nonn,mult %O A353868 1,2 %A A353868 _Max Alekseyev_, May 08 2022