OFFSET
0,2
FORMULA
a(n) = A143128(10^n).
a(n) ~ 10^(3*n) * Pi^2 / 18.
MATHEMATICA
Array[Sum[k DivisorSigma[1, k], {k, 10^#}] &, 7, 0] (* Michael De Vlieger, Nov 20 2018 *)
PROG
(PARI) a(n) = sum(k=1, 10^n, k*sigma(k)); \\ Michel Marcus, Nov 23 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Daniel Suteu, Nov 16 2018
STATUS
approved