A364212 a(n) = (1/(6*n)) * Sum_{d|n} 7^(n/d-1) * phi(7*d).

1, 4, 17, 88, 481, 2812, 16808, 102988, 640545, 4035604, 25679569, 164778696, 1064714401, 6920652008, 45214871857, 296722645888, 1954878268801, 12923917765876, 85705978837393, 569944761286648, 3799631728468936, 25388448380261788, 169992219503608177, 1140364472585830196

Offset

1,2

Links

Table of n, a(n) for n=1..24.

Formula

G.f.: (-1/6) * Sum_{k>0} phi(7*k) * log(1-7*x^k)/(7*k).

Mathematica

a[n_] := DivisorSum[n, 7^(n/#-1)*EulerPhi[7*#]/(6*n) &]; Array[a, 25] (* Amiram Eldar, Jul 14 2023 *)

Prog

(PARI) a(n) = sumdiv(n, d, 7^(n/d-1)*eulerphi(7*d))/(6*n);

Crossrefs

Cf. A000010, A359099, A359102.

Cf. A000013, A364210, A364211.

Sequence in context: A110508 A114190 A135168 * A354308 A357617 A350474

Adjacent sequences: A364209 A364210 A364211 * A364213 A364214 A364215

Keyword

nonn

Author

Seiichi Manyama, Jul 13 2023

Status

approved