OFFSET
0,2
COMMENTS
Has a symmetric representation, the same as A024916.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 0..75
FORMULA
a(n) ~ 2^(2*n-2) * Pi^2/3. - Vaclav Kotesovec, Oct 23 2023
EXAMPLE
For n = 2 the sum of all divisors of all positive integers <= 4 is [1] + [1+2] + [1+3] + [1+2+4] = 1 + 3 + 4 + 7 = 15, so a(2) = 15.
PROG
(PARI) a(n) = sum(k=1, 2^n, k*floor(2^n/k) ) \\ Jens Kruse Andersen, Jul 26 2014
(Python)
from math import isqrt
def A244824(n): return -(s:=isqrt(m:=1<<n))**2*(s+1) + sum((q:=m//k)*((k<<1)+q+1) for k in range(1, s+1))>>1 # Chai Wah Wu, Oct 23 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Jul 06 2014
EXTENSIONS
More terms from Jens Kruse Andersen, Jul 26 2014
STATUS
approved