OFFSET
1,4
COMMENTS
Multiplicative because A085731 is.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..65537
FORMULA
a(1) = 1, and for n > 1, a(n) = -Sum_{d|n, d<n} A085731(n/d) * a(d).
MAPLE
g:= proc(n) option remember;
igcd(n, n*add(i[2]/i[1], i=ifactors(n)[2]))
end:
a:= proc(n) option remember; `if`(n=1, 1, -add(
a(d)*g(n/d), d=numtheory[divisors](n) minus {n}))
end:
seq(a(n), n=1..120); # Alois P. Heinz, Jan 07 2023
MATHEMATICA
d[0] = d[1] = 0; d[n_] := n * Plus @@ ((Last[#]/First[#]) & /@ FactorInteger[n]); s[n_] := GCD[n, d[n]]; a[1] = 1; a[n_] := a[n] = -DivisorSum[n, s[n/#]*a[#] &, # < n &]; Array[a, 100] (* Amiram Eldar, Jan 07 2023 *)
CROSSREFS
KEYWORD
sign,mult
AUTHOR
Antti Karttunen, Jan 06 2023
STATUS
approved