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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 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

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