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

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =7a(5) =93a(6) =315a(7) =17a(8) =3855a(9) =13797a(10) =195a(11) =182361a(12) =41943a(13) =9709a(14) =9256395a(15) =34636833a(16) =31775a(17) =479349a(18) =1857283155a(19) =430185a(20) =26817356775a(21) =102280151421a(22) =372827a(24) =89756051247a(25) =84215045a(27) =19991120505a(28) =1205604855