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 A067709 #19 May 13 2022 07:11:40 %S A067709 2,4,16,18,64,100,450,516,1458,4096,4624,13932,14406,20124,21780, %T A067709 28900,29262,29616,36450,45996,62500,65536,92778,95916,106092,106308, %U A067709 114630,114930,121872,125652,130050,140130,145794,149124,160986,179562,185100 %N A067709 Numbers k such that phi(2*sigma(k)) = 2*sigma(phi(k)). %C A067709 Every even superperfect number (A019279) is a term of the sequence. - _Vladeta Jovovic_, Feb 11 2002 %H A067709 Amiram Eldar, <a href="/A067709/b067709.txt">Table of n, a(n) for n = 1..1000</a> %p A067709 with(numtheory); A067709:=n->`if`( phi(2*sigma(n)) = 2*sigma(phi(n)), n, NULL); seq(A067709(n), n=1..200000); # _Wesley Ivan Hurt_, Apr 07 2014 %t A067709 Select[Range[200000], EulerPhi[2*DivisorSigma[1, #]] == 2*DivisorSigma[1, EulerPhi[#]] &] (* _Amiram Eldar_, May 13 2022 *) %o A067709 (PARI) isok(k) = eulerphi(2*sigma(k)) == 2*sigma(eulerphi(k)); \\ _Michel Marcus_, May 13 2022 %Y A067709 Cf. A000010, A000203, A019279. %K A067709 nonn %O A067709 1,1 %A A067709 _Benoit Cloitre_, Feb 05 2002 %E A067709 More terms from _Vladeta Jovovic_, Feb 11 2002