A364210 a(n) = (1/(2*n)) * Sum_{d|n} 3^(n/d-1) * phi(3*d).

1, 2, 4, 8, 17, 44, 105, 278, 733, 1978, 5369, 14792, 40881, 113934, 318884, 896948, 2532161, 7174862, 20390553, 58114072, 166037460, 475473286, 1364393897, 3922640132, 11297181473, 32588043882, 94143179560, 272342824320, 788854912241, 2287679406940, 6641649422409

Offset

1,2

Links

Table of n, a(n) for n=1..31.

Formula

G.f.: (-1/2) * Sum_{k>0} phi(3*k) * log(1-3*x^k)/(3*k).

Mathematica

a[n_] := DivisorSum[n, 3^(n/#-1)*EulerPhi[3*#]/(2*n) &]; Array[a, 30] (* Amiram Eldar, Jul 14 2023 *)

Prog

(PARI) a(n) = sumdiv(n, d, 3^(n/d-1)*eulerphi(3*d))/(2*n);

Crossrefs

Cf. A000010, A034754, A195459, A327625.

Cf. A000013, A364211, A364212.

Sequence in context: A272105 A367114 A283162 * A231221 A231435 A113153

Adjacent sequences: A364207 A364208 A364209 * A364211 A364212 A364213

Keyword

nonn

Author

Seiichi Manyama, Jul 13 2023

Status

approved