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%I #10 Jun 14 2022 15:51:31
%S 0,4,12,24,48,80,168,280,576,1080,2160,4136,8448,16432,33096,65760,
%T 131712,262208,525672,1048648,2099520,4194960,8392824,16777304,
%U 33564096,67109200,134234256,268437672,536904480,1073741936,2147554080,4294967416,8590066944
%N a(n) = Sum_{d|n} phi(n/d)*2^(d+1), with a(0) = 0.
%H G. C. Greubel, <a href="/A160619/b160619.txt">Table of n, a(n) for n = 0..1000</a>
%F a(n) = 4*A034738(n). - _Michel Marcus_, May 07 2018
%t a[n_]:= If[n<1, 0, Sum[EulerPhi[n/d] 2^(d+1), {d, Divisors[n]}]]; Table[a[n], {n, 0, 50}] (* _G. C. Greubel_, May 06 2018 *)
%o (PARI) a(n) = if (n==0, 0, sumdiv(n, d, eulerphi(n/d)*2^(d+1))); \\ _Michel Marcus_, May 07 2018; corrected Jun 14 2022
%Y Cf. A034738, A053635, A161219.
%K nonn
%O 0,2
%A _N. J. A. Sloane_, Nov 21 2009
%E Name edited by _Michel Marcus_, Jun 14 2022
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