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 A067781 #24 May 08 2025 06:51:01
%S A067781 1,170,364,679,5044,5130,5670,5770,8721,8736,9154,9639,9809,14322,
%T A067781 16376,22413,27783,30256,32025,37114,38760,51455,71604,78570,82615,
%U A067781 88392,92004,100821,101153,104168,115430,121056,133569,139954,148568,171069,177940,198462,217868
%N A067781 Numbers k such that phi(k) and sigma(k) are both perfect squares.
%C A067781 A subsequence of A011257. - _M. F. Hasler_, Sep 22 2009
%H A067781 Donovan Johnson, <a href="/A067781/b067781.txt">Table of n, a(n) for n = 1..5000</a>
%F A067781 Equals A006532 intersect A039770. - _M. F. Hasler_, Sep 22 2009
%t A067781 Select[Range[250000], And @@ (IntegerQ[Sqrt[#1]] & /@ {EulerPhi[#], DivisorSigma[1, #]} ) &] (* _Amiram Eldar_, May 08 2025 *)
%o A067781 (PARI) isok(k) = {my(f = factor(k)); issquare(eulerphi(f)) && issquare(sigma(f));} \\ _Amiram Eldar_, May 08 2025
%Y A067781 Cf. A000010 (phi), A000203 (sigma), A006532, A011257, A039770.
%K A067781 nonn
%O A067781 1,2
%A A067781 _Benoit Cloitre_, Feb 07 2002