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 A330701 #12 Sep 12 2020 03:21:03 %S A330701 26,39,45,51,52,58,74,82,98,104,111,116,135,142,146,147,148,164,178, %T A330701 195,196,208,219,232,284,286,292,296,328,356,357,386,392,405,406,416, %U A330701 435,464,495,555,561,568,572,574,579,584,585,592,598,615,622,638,646,650 %N A330701 Numbers k such that psi(phi(k)) = 2 * phi(psi(k)), where psi(k) is the Dedekind psi function (A001615) and phi(k) is the Euler totient function (A000010). %C A330701 Sandor proved that this sequence is infinite. %H A330701 Amiram Eldar, <a href="/A330701/b330701.txt">Table of n, a(n) for n = 1..10000</a> %H A330701 Jozsef Sandor, <a href="https://www.emis.de/journals/JIPAM/article546.html">On the composition of some arithmetic functions, II</a>, Journal of Inequalities in Pure and Applied Mathematics, Vol. 6, No. 3 (2005), Article 73. %e A330701 26 is in the sequence since psi(phi(26)) = psi(12) = 24, and 2 * phi(psi(26)) = 2 * phi(42) = 2 * 12 = 24. %t A330701 psi[1] = 1; psi[n_] := n * Times @@ (1 + 1/Transpose[FactorInteger[n]][[1]]); Select[Range[1000], psi[EulerPhi[#]] == 2 * EulerPhi[psi[#]] &] %Y A330701 Cf. A000010, A001615, A290002. %K A330701 nonn %O A330701 1,1 %A A330701 _Amiram Eldar_, Dec 26 2019