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A099979
Bisection of A001157: sigma_2(2n).
3
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
1,1
LINKS
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
Sigma_2(k*n): A001157 (k=1), this sequence (k=2), A283237 (k=3).
Sequence in context: A022268 A201279 A146721 * A366723 A039659 A147238
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