



1, 2, 4, 11, 28, 152, 726, 5268, 40438, 365944, 3628810, 39974466, 479001612, 6228256404, 87178339984, 1307706805928, 20922789888016, 355688409760972, 6402373705728018, 121645133931170028, 2432902008232456692
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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_{dn} 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] (* JeanFrançois Alcover, Mar 06 2016 *)


CROSSREFS

A061860[p] = A061417[p] = (p1)!+(p1) 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



