OFFSET
1,2
FORMULA
G.f.: Sum_{k>0} 2^(k-1) * x^(2*k-1) / (1 - x^(2*k-1))^2.
a(n) = Sum_{d|n, d odd} 2^((d-1)/2) * (n/d).
MATHEMATICA
a[n_] := DivisorSum[n, 2^((#-1)/2) * (n/#) &, OddQ[#] &]; Array[a, 50] (* Amiram Eldar, Jul 02 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (d%2==1)*2^((d-1)/2)*n/d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 02 2023
STATUS
approved