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%I #12 Aug 23 2015 03:27:15
%S 1,2,16,188,2896,50452,953056,19003476,394397776,8439756848,
%T 185033251616,4137181680700,94020327215200,2166105078791448,
%U 50489825388328608,1188777328563914488,28236363841989180496,675879582290807439796,16289254212704277185152
%N Number of distinct (n red, n blue, n green)-bead necklaces.
%H Alois P. Heinz, <a href="/A118644/b118644.txt">Table of n, a(n) for n = 0..700</a>
%F Sum_{d|n} ( phi(n/d)(3d Choose d)(2d Choose d) )/3n for n>0. [Corrected by several correspondents, Mar 04 2010]
%F a(n) ~ 3^(3*n-1/2) / (2*Pi*n^2). - _Vaclav Kotesovec_, Aug 23 2015
%t f[n_] := Plus @@ (EulerPhi[n/# ]Binomial[3#, # ]Binomial[2#, # ] & /@ Divisors[n])/(3n)
%Y Cf. A003239.
%Y Column k=3 of A208183.
%K easy,nonn
%O 0,2
%A _Jacob A. Siehler_, May 10 2006
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