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 A291167 #16 Jul 23 2021 02:08:25
%S A291167 1,3,18,20,22,27,60,66,70,72,80,88,92,94,99,115,119,162,170,210,212,
%T A291167 214,217,240,243,252,264,265,276,280,282,288,308,310,315,320,322,345,
%U A291167 352,357,368,376,382,385,423,497,500,510,517,527,540,594,596,612,636,637,642,648,651,679,680,710,725,742
%N A291167 Numbers k such that psi(k) is a perfect square where psi(k) = A001615(k).
%C A291167 The product of an even number of distinct members of A066436 is in the sequence. - _Robert Israel_, Aug 22 2017
%H A291167 Robert Israel, <a href="/A291167/b291167.txt">Table of n, a(n) for n = 1..10000</a>
%e A291167 60 is a term because psi(60) = 144 is a perfect square.
%p A291167 filter:= proc(n) issqr(n*mul(1+1/p,p=numtheory:-factorset(n))) end proc:
%p A291167 select(filter, [$1..1000]); # _Robert Israel_, Aug 22 2017
%t A291167 Select[Range@ 750, IntegerQ@ Sqrt[# Sum[MoebiusMu[d]^2/d, {d, Divisors@ #}]] &] (* _Michael De Vlieger_, Aug 19 2017 *)
%o A291167 (PARI) a001615(n) = n*sumdivmult(n, d, issquarefree(d)/d);
%o A291167 is(n) = issquare(a001615(n));
%Y A291167 Cf. A001615, A006532, A066436.
%K A291167 nonn,easy
%O A291167 1,2
%A A291167 _Altug Alkan_, Aug 19 2017