OFFSET
0,2
COMMENTS
a(n) ~ 10^(3n)*zeta(3)/3.
LINKS
Hiroaki Yamanouchi, Table of n, a(n) for n = 0..18
MATHEMATICA
k = 1; lst = {}; s = 0; Do[ While[k < 10^n + 1, s = s + DivisorSigma[2, k]; k++]; AppendTo[lst, s], {n, 0, 9}]; lst
a[n_] := With[{nn=10^n}, Sum[Floor[nn/k]*k^2, {k, nn}]]; Array[a, 9, 0] (* T. D. Noe, Apr 25 2011 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Apr 25 2011
EXTENSIONS
a(10)-a(11) from Hiroaki Yamanouchi, Jul 06 2014
STATUS
approved