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Lerch's function q_2(n) = (2^{phi(t)} - 1)/t where t = 2*n - 1.
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%I #21 Dec 19 2017 02:23:04

%S 1,1,3,9,7,93,315,17,3855,13797,195,182361,41943,9709,9256395,

%T 34636833,31775,479349,1857283155,430185,26817356775,102280151421,

%U 372827,1497207322929,89756051247,84215045,84973577874915,19991120505,1205604855,4885260612740877

%N Lerch's function q_2(n) = (2^{phi(t)} - 1)/t where t = 2*n - 1.

%C Lerch defines q_u = (u^phi(p) - 1)/p for any odd integer p and for u prime to p. - _Altug Alkan_, Dec 19 2017

%D L. E. Dickson, History of the Theory of Numbers. Carnegie Institute Public. 256, Washington, DC, Vol. 1, 1919; Vol. 2, 1920; Vol. 3, 1923, see vol. 1, p. 109.

%H T. D. Noe, <a href="/A001226/b001226.txt">Table of n, a(n) for n = 1..200</a>

%H R. C. Read, <a href="/A000684/a000684_1.pdf">Letter to N. J. A. Sloane, Oct. 29, 1976</a>

%t Table[(2^EulerPhi[n] - 1)/n, {n, 1, 40, 2}] (* _T. D. Noe_, Jun 26 2012 *)

%o (PARI) a(n) = (2^eulerphi(2*n-1) - 1)/(2*n-1) \\ _Andrew Howroyd_, Dec 18 2017

%Y Cf. A000010.

%K nonn

%O 1,3

%A _N. J. A. Sloane_