A364211 a(n) = (1/(4*n)) * Sum_{d|n} 5^(n/d-1) * phi(5*d).

1, 3, 9, 33, 126, 527, 2233, 9783, 43409, 195378, 887785, 4069297, 18780049, 87194199, 406901134, 1907353533, 8975758273, 42385547227, 200773540297, 953674414158, 4541306270097, 21674416725855, 103660251783289, 496705375169547, 2384185791015751, 11462431696965147, 55189485903168409

Offset

1,2

Links

Table of n, a(n) for n=1..27.

Formula

G.f.: (-1/4) * Sum_{k>0} phi(5*k) * log(1-5*x^k)/(5*k).

Mathematica

a[n_] := DivisorSum[n, 5^(n/#-1)*EulerPhi[5*#]/(4*n) &]; Array[a, 25] (* Amiram Eldar, Jul 14 2023 *)

Prog

(PARI) a(n) = sumdiv(n, d, 5^(n/d-1)*eulerphi(5*d))/(4*n);

Crossrefs

Cf. A000010, A343492, A359100, A359101.

Cf. A000013, A364210, A364212.

Sequence in context: A049157 A138178 A063027 * A148998 A049185 A049162

Adjacent sequences: A364208 A364209 A364210 * A364212 A364213 A364214

Keyword

nonn

Author

Seiichi Manyama, Jul 13 2023

Status

approved