A099979 Bisection of A001157: sigma_2(2n).

5, 21, 50, 85, 130, 210, 250, 341, 455, 546, 610, 850, 850, 1050, 1300, 1365, 1450, 1911, 1810, 2210, 2500, 2562, 2650, 3410, 3255, 3570, 4100, 4250, 4210, 5460, 4810, 5461, 6100, 6090, 6500, 7735, 6850, 7602, 8500, 8866, 8410, 10500, 9250, 10370

Offset: 1

Author

N. J. A. Sloane, Nov 19 2004

Keywords

• nonn
• easy

Examples

			a(1) = sigma_2(2*1) = 1 + 2^2 = 5.
a(2) = sigma_2(2*2) = 1 + 2^2 + 4^2 = 21.
		

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..10000

Crossrefs

Sigma_2(k*n): A001157 (k=1), this sequence (k=2), A283237 (k=3).

Programs

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 *)

PARI

a(n) = sigma(2*n,2); \\ Indranil Ghosh, Mar 03 2017

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

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