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A061860 Variant of A061417. 2
1, 2, 4, 11, 28, 152, 726, 5268, 40438, 365944, 3628810, 39974466, 479001612, 6228256404, 87178339984, 1307706805928, 20922789888016, 355688409760972, 6402373705728018, 121645133931170028, 2432902008232456692 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Does this count some variety of necklaces?

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..445

FORMULA

a(n) = (1/n)*Sum_{d|n} phi(n/d)*C(n, d)*(d!).

MAPLE

[seq(A061860(j), j=1..40)]; with(numtheory); A061860 := proc(n) local d, s; s := 0; for d in divisors(n) do s := s + phi(n/d)*(binomial(n, d))*(d!); od; RETURN(s/n); end;

MATHEMATICA

a[n_] := DivisorSum[n, EulerPhi[n/#] Binomial[n, #] (#!)&]/n; Array[a, 25] (* Jean-François Alcover, Mar 06 2016 *)

CROSSREFS

A061860[p] = A061417[p] = (p-1)!+(p-1) for all prime p's.

Sequence in context: A005503 A148139 A336871 * A093960 A267912 A118311

Adjacent sequences:  A061857 A061858 A061859 * A061861 A061862 A061863

KEYWORD

nonn

AUTHOR

Antti Karttunen, May 11 2001

STATUS

approved

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Last modified December 2 05:01 EST 2021. Contains 349437 sequences. (Running on oeis4.)