COMMENTS
Equivalently: subsequence of A000203 (sigma) with indices equal to a square or twice a square (A028982).
CROSSREFS
Equivalently: subsequence of Cf. A000203 (sigma = sum-of-divisors function) with indices equal to a square or twice a square , A152678 (even terms in A000203), A028982 (squares and twice the squares).
Cf. A152678 (even terms in A000203).
COMMENTS
Equivalently: subsequence of A000203 (sigma) with indices equal to a square or twice a square (A028982).
CROSSREFS
Cf. Equivalently: subsequence of A000203 (sigma = sum-of-divisors function), A152678 with indices equal to a square or twice a square (even terms in A000203), A028982 (squares and twice the squares).
Cf. A152678 (even terms in A000203).
LINKS
Amiram Eldar, <a href="/A152677/b152677_1.txt">Table of n, a(n) for n = 1..10000</a>
Discussion
Tue Nov 28
11:00
OEIS Server: Installed first b-file as b152677.txt.
Discussion
Tue Nov 28
10:56
Michel Marcus: transform 1st comment into a xref ?
FORMULA
Sum_{k=1..n} a(k) ~ c * n^3, where c = (16-10*sqrt(2))*zeta(3)/Pi^2 = 0.226276... . - Amiram Eldar, Nov 28 2023
MATHEMATICA
With[{max = 1000}, DivisorSigma[1, Union[Range[Sqrt[max]]^2, 2*Range[Sqrt[max/2]]^2]]] (* Amiram Eldar, Nov 28 2023 *)
LINKS
Amiram Eldar, <a href="/A152677/b152677_1.txt">Table of n, a(n) for n = 1..10000</a>
PROG
(MAGMAMagma) [d:k in [1..1000]|IsOdd(d) where d is DivisorSigma(1, k)]; // Marius A. Burtea, Jan 09 2020
Discussion
Thu Sep 08
08:45
OEIS Server: https://oeis.org/edit/global/2944
