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A364212 a(n) = (1/(6*n)) * Sum_{d|n} 7^(n/d-1) * phi(7*d). 2
1, 4, 17, 88, 481, 2812, 16808, 102988, 640545, 4035604, 25679569, 164778696, 1064714401, 6920652008, 45214871857, 296722645888, 1954878268801, 12923917765876, 85705978837393, 569944761286648, 3799631728468936, 25388448380261788, 169992219503608177, 1140364472585830196 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
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
Sequence in context: A110508 A114190 A135168 * A354308 A357617 A350474
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 13 2023
STATUS
approved

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Last modified May 21 15:47 EDT 2024. Contains 372738 sequences. (Running on oeis4.)