OFFSET
1,2
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.
MATHEMATICA
a[n_] := Sum[(3/2 + 1/2 (-1)^Mod[d, 2]) DivisorSigma[1, n/d], {d, Divisors[ n]}] - If[OddQ[n], 0, Sum[(3/2 + 1/2 (-1)^Mod[d, 2]) DivisorSigma[1, n/(2 d)], {d, Divisors[n/2]}]];
Array[a, 59] (* Jean-François Alcover, Oct 10 2018, after Gheorghe Coserea *)
PROG
(PARI)
a(n) = {
sumdiv(n, d, (3/2 + 1/2*(-1)^(d%2)) * sigma(n/d)) -
if (n%2, 0, sumdiv(n\2, d, (3/2 + 1/2*(-1)^(d%2))*sigma(n\(2*d))))
};
vector(59, n, a(n)) \\ Gheorghe Coserea, May 04 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Oct 28 2015
EXTENSIONS
More terms from Gheorghe Coserea, May 04 2016
STATUS
approved