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%I #13 May 10 2024 09:25:50
%S 1,2,2,4,4,4,7,8,6,8,10,8,12,14,8,16,16,12,18,16,14,20,22,16,20,24,18,
%T 28,28,16,30,32,20,32,28,24,36,36,24,32,40,28,42,40,24,44,46,32,49,40,
%U 32,48,52,36,40,56,36,56,58,32,60,60,42,64,48,40,66,64,44,56,70,48,72,72,40,72,70,48
%N a(n) = phi(14 * n)/6.
%F G.f.: Sum_{k>=1} mu(14 * k) * x^k / (1 - x^k)^2, where mu() is the Moebius function (A008683).
%F Multiplicative with a(p^e) = p^e if p = 2 or 7, and (p-1)*p^(e-1) otherwise.
%F Sum_{k=1..n} a(k) ~ (49/(12*Pi^2)) * n^2. - _Amiram Eldar_, May 10 2024
%t a[n_] := EulerPhi[14 * n]/6; Array[a, 100] (* _Amiram Eldar_, May 10 2024 *)
%o (PARI) a(n) = eulerphi(14*n)/6;
%o (PARI) my(N=80, x='x+O('x^N)); Vec(sum(k=1, N, moebius(14*k)*x^k/(1-x^k)^2))
%Y Column k=14 of A372673.
%Y Cf. A008683.
%K nonn,mult,easy
%O 1,2
%A _Seiichi Manyama_, May 10 2024
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