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A373925
a(n) = Sum_{d|n} (-1)^phi(d).
2
-1, -2, 0, -1, 0, 0, 0, 0, 1, 0, 0, 2, 0, 0, 2, 1, 0, 2, 0, 2, 2, 0, 0, 4, 1, 0, 2, 2, 0, 4, 0, 2, 2, 0, 2, 5, 0, 0, 2, 4, 0, 4, 0, 2, 4, 0, 0, 6, 1, 2, 2, 2, 0, 4, 2, 4, 2, 0, 0, 8, 0, 0, 4, 3, 2, 4, 0, 2, 2, 4, 0, 8, 0, 0, 4, 2, 2, 4, 0, 6, 3, 0, 0, 8, 2, 0, 2, 4, 0
OFFSET
1,2
COMMENTS
Inverse Möbius transform of (-1)^phi(n) (which equals -1 if 1 <= n <= 2, and 1 if n >= 3).
LINKS
FORMULA
a(n) = A000005(n) - 3 - (-1)^n. - Robert Israel, Sep 13 2024
MAPLE
f:= proc(n) local d; add(q(d), d = numtheory:-divisors(n)) end proc:
map(f, [$1..100]); # Robert Israel, Sep 13 2024
MATHEMATICA
Table[DivisorSum[n, (-1)^EulerPhi[#] &], {n, 100}]
CROSSREFS
Cf. A000005, A000010 (phi), A373926.
Sequence in context: A070103 A113048 A331671 * A123758 A231642 A288318
KEYWORD
sign
AUTHOR
Wesley Ivan Hurt, Jun 22 2024
STATUS
approved