OFFSET
1,4
MATHEMATICA
l[n_]:=Sum[(-1)^(k-1), {k, Select[Range[n], And[SquareFreeQ[#], GCD[n, #]==1]&]}];
Table[l[n], {n, 100}]
PROG
(PARI) a(n) = sum(k=1, n, if (issquarefree(k) && (gcd(n, k)==1), (-1)^(k-1))); \\ Michel Marcus, May 15 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, May 14 2018
STATUS
approved