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%I #24 Dec 01 2018 19:56:32
%S 1,0,5,2,7,0,9,6,18,0,13,10,15,0,35,14,19,0,21,14,45,0,25,30,38,0,58,
%T 18,31,0,33,30,65,0,63,36,39,0,75,42,43,0,45,26,126,0,49,70,66,0,95,
%U 30,55,0,91,54,105,0,61,70,63,0,162,62,105,0,69
%N The number c_{Cc,pi_1(B_2)}(n) of the second amphicosm n-coverings over the second amphicosm.
%H Gheorghe Coserea, <a href="/A263832/b263832.txt">Table of n, a(n) for n = 1..20000</a>
%H G. Chelnokov, M. Deryagina, A. Mednykh, <a href="http://arxiv.org/abs/1502.01528">On the Coverings of Amphicosms; Revised title: On the coverings of Euclidian manifolds B_1 and B_2</a>, arXiv preprint arXiv:1502.01528 [math.AT], 2015.
%H G. Chelnokov, M. Deryagina and A. Mednykh, <a href="https://doi.org/10.1080/00927872.2016.1222396">On the coverings of Euclidean manifolds B_1 and B_2</a>, Communications in Algebra, Vol. 45, No. 4 (2017), 1558-1576.
%t sigma[n_] := DivisorSigma[1, n]; q = Quotient;
%t a[n_] := Switch[Mod[n, 4], 0, Sum[sigma[q[n, 2d]] - sigma[q[n, 4d]], {d, Divisors[q[n, 4]]}], 2, 0, 1|3, Sum[sigma[d], {d, Divisors[n]}]];
%t Array[a, 70] (* _Jean-François Alcover_, Dec 01 2018, after _Gheorghe Coserea_ *)
%o (PARI)
%o A007429(n) = sumdiv(n, d, sigma(d));
%o a(n) = {
%o if (n%2, A007429(n), if (n%4, 0,
%o sumdiv(n\4, d, sigma(n\(2*d)) - sigma(n\(4*d)))));
%o };
%o vector(67, n, a(n)) \\ _Gheorghe Coserea_, May 05 2016
%Y Cf. A263825, A263826, A263827, A263828, A263829, A263830, A263831.
%K nonn
%O 1,3
%A _N. J. A. Sloane_, Oct 28 2015
%E More terms from _Gheorghe Coserea_, May 05 2016
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