OFFSET
2,1
FORMULA
G.f.: (1/(1 - x)) * Sum_{k>=2} k*x^k/(1 - x^k). - Ilya Gutkovskiy, Sep 02 2019
MATHEMATICA
Table[Sum[k*Floor[n/k], {k, 2, n}], {n, 2, 60}] (* Harvey P. Dale, Mar 13 2015 *)
PROG
(Magma) [&+[k*Floor(n/k): k in [2..n]]: n in [2..55]]; // Bruno Berselli, Jan 08 2012
(PARI) a(n) = sum(k=2, n, k*floor(n/k)); \\ Michel Marcus, Sep 02 2019
(Python)
from math import isqrt
def A024917(n): return (-(s:=isqrt(n))**2*(s+1)+sum((q:=n//k)*((k<<1)+q+1) for k in range(1, s+1))>>1)-n # Chai Wah Wu, Oct 23 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved