OFFSET
1,3
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = phi(n) if n odd, phi(n) - phi(n/2) if n even, where phi = A000010.
a(n) = Sum_{d|n} mu(n/d) * A026741(d).
a(n) = Sum_{d|n} A092673(n/d) * d.
a(p) = p - 1, where p is odd prime.
Product_{n>=1} 1 / (1 - x^n)^a(n) = g.f. for A299069.
Sum_{k=1..n} a(k) ~ 9*n^2 / (4*Pi^2). - Vaclav Kotesovec, Oct 26 2019
Multiplicative with a(2^e) = 0 if e = 1 and 2^(e-2) otherwise, and a(p^e) = (p-1)*p^(e-1) for odd primes p. - Amiram Eldar, Nov 30 2020
MATHEMATICA
Table[Sum[MoebiusMu[n/d] Numerator[d/2], {d, Divisors[n]}], {n, 1, 75}]
a[n_] := If[OddQ[n], EulerPhi[n], EulerPhi[n] - EulerPhi[n/2]]; Table[a[n], {n, 1, 75}]
f[2, e_] := If[e == 1, 0, 2^(e - 2)]; f[p_, e_] := (p - 1)*p^(e - 1); a[1] = 1; a[n_] := Times @@ (f @@@ FactorInteger[n]); Array[a, 100] (* Amiram Eldar, Nov 30 2020 *)
PROG
(Magma) [IsOdd(n) select EulerPhi(n) else EulerPhi(n)-EulerPhi(n div 2) : n in [1..80]]; // Marius A. Burtea, Oct 17 2019
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
Ilya Gutkovskiy, Oct 17 2019
STATUS
approved