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 A080402 #15 Aug 12 2024 09:35:05
%S A080402 6,7,14,15,21,24,26,27,28,30,33,34,35,36,39,41,42,43,45,46,51,54,55,
%T A080402 56,57,60,63,65,66,69,70,74,77,78,81,82,84,85,86,87,90,91,93,94,95,96,
%U A080402 100,102,104,105,106,107,108,110,111,112,114,115,119,120,123,125,126,129
%N A080402 Numbers k such that the sum of the squares of the divisors of k (A001157(k)) is not squarefree.
%H A080402 Amiram Eldar, <a href="/A080402/b080402.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Harvey P. Dale)
%F A080402 mu(sigma_2(a(n))) = 0.
%t A080402 Do[s=MoebiusMu[DivisorSigma[2, n]]; If[Equal[s, 0], Print[n]], {n, 1, 1000}]
%t A080402 Select[Range[130],!SquareFreeQ[DivisorSigma[2,#]]&] (* _Harvey P. Dale_, Oct 10 2011 *)
%o A080402 (PARI) is(k) = !issquarefree(sigma(k, 2)); \\ _Amiram Eldar_, Aug 12 2024
%Y A080402 Cf. A001157, A005117, A013929, A065300, A080401 (complement).
%K A080402 nonn
%O A080402 1,1
%A A080402 _Labos Elemer_, Mar 19 2003