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A160890 a(n) = ((2^b-1)/phi(n))*Sum_{d|n} Moebius(n/d)*d^(b-1) for b = 3. 1
7, 21, 28, 42, 42, 84, 56, 84, 84, 126, 84, 168, 98, 168, 168, 168, 126, 252, 140, 252, 224, 252, 168, 336, 210, 294, 252, 336, 210, 504, 224, 336, 336, 378, 336, 504, 266, 420, 392, 504, 294, 672, 308, 504, 504, 504, 336, 672, 392, 630, 504, 588, 378, 756 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16384

J. H. Kwak and J. Lee, Enumeration of graph coverings, surface branched coverings and related group theory, in Combinatorial and Computational Mathematics (Pohang, 2000), ed. S. Hong et al., World Scientific, Singapore 2001, pp. 97-161. See p. 134.

MATHEMATICA

With[{b = 3}, Table[((2^b - 1)/EulerPhi[n]) DivisorSum[n, MoebiusMu[n/#] #^(b - 1) &], {n, 54}]] (* Michael De Vlieger, Nov 23 2017 *)

PROG

(PARI) A160890(n) = ((7/eulerphi(n))*sumdiv(n, d, moebius(n/d)*(d^2))); \\ Antti Karttunen, Nov 23 2017

CROSSREFS

Sequence in context: A219036 A063469 A155131 * A319527 A297178 A032639

Adjacent sequences:  A160887 A160888 A160889 * A160891 A160892 A160893

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Nov 19 2009

STATUS

approved

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Last modified April 18 14:46 EDT 2019. Contains 322209 sequences. (Running on oeis4.)