OFFSET
1,6
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
a(1) = 1; a(n) = -Sum_{d|n, d < n} phi(d) * a(d).
MAPLE
f:= proc(n) option remember; local G, g;
G:= subs(1=NULL, map(igcd, [$1..n], n));
-add(procname(n/g), g=G);
end proc:
f(1):= 1:
map(f, [$1..100]); # Robert Israel, Dec 21 2022
MATHEMATICA
a[1] = 1; a[n_] := a[n] = -Sum[If[GCD[n, k] > 1, a[n/GCD[n, k]], 0], {k, 1, n}]; Table[a[n], {n, 1, 70}]
a[1] = 1; a[n_] := -Sum[If[d < n, EulerPhi[d] a[d], 0], {d, Divisors[n]}]; Table[a[n], {n, 1, 70}]
CROSSREFS
KEYWORD
sign,look
AUTHOR
Ilya Gutkovskiy, Apr 28 2021
STATUS
approved