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
Keywords
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.
Programs
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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 *) -
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
Extensions
More terms from Gheorghe Coserea, May 05 2016