A263832 The number c_{Cc,pi_1(B_2)}(n) of the second amphicosm n-coverings over the second amphicosm.

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, 18, 31, 0, 33, 30, 65, 0, 63, 36, 39, 0, 75, 42, 43, 0, 45, 26, 126, 0, 49, 70, 66, 0, 95, 30, 55, 0, 91, 54, 105, 0, 61, 70, 63, 0, 162, 62, 105, 0, 69

Offset

1,3

Links

Gheorghe Coserea, Table of n, a(n) for n = 1..20000

G. Chelnokov, M. Deryagina, A. Mednykh, On the Coverings of Amphicosms; Revised title: On the coverings of Euclidian manifolds B_1 and B_2, arXiv preprint arXiv:1502.01528 [math.AT], 2015.

G. Chelnokov, M. Deryagina and A. Mednykh, On the coverings of Euclidean manifolds B_1 and B_2, Communications in Algebra, Vol. 45, No. 4 (2017), 1558-1576.

Mathematica

sigma[n_] := DivisorSigma[1, n]; q = Quotient;
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]}]];
Array[a, 70] (* Jean-François Alcover, Dec 01 2018, after Gheorghe Coserea *)

Prog

(PARI)
A007429(n) = sumdiv(n, d, sigma(d));
a(n) = {
  if (n%2, A007429(n), if (n%4, 0,
      sumdiv(n\4, d, sigma(n\(2*d)) - sigma(n\(4*d)))));
};
vector(67, n, a(n))  \\ Gheorghe Coserea, May 05 2016

Crossrefs

Cf. A263825, A263826, A263827, A263828, A263829, A263830, A263831.

Sequence in context: A180706 A108399 A094772 * A351952 A342002 A344760

Adjacent sequences: A263829 A263830 A263831 * A263833 A263834 A263835

Keyword

nonn

Author

N. J. A. Sloane, Oct 28 2015

Extensions

More terms from Gheorghe Coserea, May 05 2016

Status

approved