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A099978
Bisection of A001157: a(n) = sigma_2(2n-1).
2
1, 10, 26, 50, 91, 122, 170, 260, 290, 362, 500, 530, 651, 820, 842, 962, 1220, 1300, 1370, 1700, 1682, 1850, 2366, 2210, 2451, 2900, 2810, 3172, 3620, 3482, 3722, 4550, 4420, 4490, 5300, 5042, 5330, 6510, 6100, 6242, 7381, 6890, 7540, 8420, 7922, 8500
OFFSET
1,2
LINKS
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)
MAPLE
with(numtheory): A099978 := n->sigma[2](2*n-1): seq(A099978(n), n=1..60);
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
Cf. A099979(n) = sigma_2(2n), the other bisection of A001157.
Sequence in context: A198017 A137351 A134406 * A242719 A242489 A074789
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