OFFSET
1,1
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A001157(2*n) = sigma_2(2*n).
Sum_{k=1..n} a(k) ~ 3 * zeta(3) * n^3 / 2. - Vaclav Kotesovec, Aug 07 2022
EXAMPLE
a(1) = sigma_2(2*1) = 1 + 2^2 = 5.
a(2) = sigma_2(2*2) = 1 + 2^2 + 4^2 = 21.
MAPLE
with(numtheory): seq(sigma[2](2*n), n=1..50); # C. Ronaldo
MATHEMATICA
Table[DivisorSigma[2, 2n], {n, 1, 47}] (* Indranil Ghosh, Mar 03 2017 *)
PROG
(PARI) a(n) = sigma(2*n, 2); \\ Indranil Ghosh, Mar 03 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 19 2004
EXTENSIONS
More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Jan 18 2005
Offset changed to 1 by Seiichi Manyama, Mar 03 2017
Examples added and name edited by M. F. Hasler, Mar 06 2017
STATUS
approved