OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A001157(2n-1) = sigma_2(2n-1). - M. F. Hasler, Mar 06 2017
Sum_{k=1..n} a(k) ~ 7*zeta(3)*n^3/6. - Vaclav Kotesovec, Aug 07 2022
EXAMPLE
From M. F. Hasler, Mar 06 2017: (Start)
a(1) = sigma_2(2*1-1) = 1.
a(2) = sigma_2(2*2-1) = 1 + 3^2 = 10.
a(5) = sigma_2(2*5-1) = 1 + 3^2 + 9^2 = 91. (End)
MATHEMATICA
DivisorSigma[2, Range[1, 91, 2]] (* Amiram Eldar, Aug 17 2019 *)
PROG
(PARI) A099978(n)=sigma(2*n-1, 2) \\ M. F. Hasler, Mar 06 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 19 2004
EXTENSIONS
More terms from Emeric Deutsch, Dec 07 2004
Edited by M. F. Hasler, Mar 06 2017
STATUS
approved