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%I #18 Feb 17 2021 04:05:21
%S 28,56,153,172,173,175,176,177,178,180,181,344,351,352,353,354,356,
%T 357,361,362,363,365,366,367,368,370,371,373,374,375,383,386,391,393,
%U 394,395,396,397,400,405,408,425,428,640,752,848,849,850,851,852,853,854
%N Numbers k such that Sum_{j=1..k} mu(j)^2 = floor(6*k/Pi^2).
%H Amiram Eldar, <a href="/A068576/b068576.txt">Table of n, a(n) for n = 1..10000</a>
%t seq[max_] := Flatten @ Position[Accumulate @ Array[Boole @ SquareFreeQ[#] &, max] - Floor[6*Range[max]/Pi^2], 0]; seq[1000] (* _Amiram Eldar_, Feb 17 2021 *)
%o (PARI) isok(k) = sum(j=1, k, moebius(j)^2) == 6*k\Pi^2; \\ _Michel Marcus_, Feb 15 2021
%Y Cf. A008683, A013928, A059956.
%K easy,nonn
%O 1,1
%A _Benoit Cloitre_, Mar 26 2002