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%I #31 Mar 09 2021 04:07:19
%S 0,3,6,11,16,23,31,39,50,61,75,89,103,120,139,157,177,199,219,243,269,
%T 297,323,351,381,412,444,477,513,547,584,624,660,703,745,789,835,882,
%U 928,977,1025,1073,1124,1174,1230,1285,1342,1400,1460,1523,1582,1645,1708
%N Number of squarefree positive integers less than n^2.
%H Jason Kimberley, <a href="/A278100/b278100.txt">Table of n, a(n) for n = 1..5000</a>
%F a(n) = A013928(n^2).
%F a(n) ~ 6*n^2/Pi^2 + O(n). - _Amiram Eldar_, Mar 09 2021
%t Table[Count[Range[n^2], k_ /; SquareFreeQ@ k], {n, 53}] (* _Michael De Vlieger_, Nov 24 2016 *)
%t Module[{nn=60,sf},sf=Accumulate[Table[If[SquareFreeQ[n],1,0],{n,0,nn^2}]];Table[sf[[k^2]],{k,nn}]] (* _Harvey P. Dale_, Nov 14 2020 *)
%o (Magma)
%o A278100:=func<n|#[k:k in[1..n^2-1]|IsSquarefree(k)]>;
%o [A278100(n):n in[1..53]]; // in cubic time
%o (PARI) a(n) = #select(x->issquarefree(x), vector(n^2-1, k, k)); \\ _Michel Marcus_, Nov 12 2016
%Y Cf. A005117, A013928, A059956.
%Y This is the row length sequence of A277648 and A278101.
%K nonn,easy
%O 1,2
%A _Jason Kimberley_, Nov 12 2016
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