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%I #9 May 15 2018 08:32:49
%S 1,1,0,2,1,2,1,4,2,3,1,4,2,5,2,7,3,6,4,7,4,9,5,8,5,10,3,9,5,8,5,13,5,
%T 13,5,11,7,15,5,14,8,11,8,17,6,18,8,15,8,17,7,19,10,16,9,20,9,23,12,
%U 15,13,25,8,26,10,18,13,26,11,22,14,22,15,30,9,29
%N a(n) = Sum_{k < n, k squarefree and relatively prime to n} (-1)^(k-1).
%t l[n_]:=Sum[(-1)^(k-1),{k,Select[Range[n],And[SquareFreeQ[#],GCD[n,#]==1]&]}];
%t Table[l[n],{n,100}]
%o (PARI) a(n) = sum(k=1, n, if (issquarefree(k) && (gcd(n,k)==1), (-1)^(k-1))); \\ _Michel Marcus_, May 15 2018
%Y Cf. A000010, A001221, A005117, A008683, A073311, A111972, A112399, A139555, A265675, A304573, A304574, A304575.
%K nonn
%O 1,4
%A _Gus Wiseman_, May 14 2018
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