OFFSET
1,6
LINKS
FORMULA
a(1) = 1, and for n > 1, a(n) = -Sum_{d|n, d<n} A009194(n/d) * a(d).
MATHEMATICA
s[n_] := GCD[n, DivisorSigma[1, n]]; a[1] = 1; a[n_] := - DivisorSum[n, a[#] * s[n/#] &, # < n &]; Array[a, 100] (* Amiram Eldar, Jul 20 2022 *)
PROG
CROSSREFS
KEYWORD
sign
AUTHOR
Antti Karttunen, Jul 20 2022
STATUS
approved