A356533 a(n) = sigma_2(n)^2.
1, 25, 100, 441, 676, 2500, 2500, 7225, 8281, 16900, 14884, 44100, 28900, 62500, 67600, 116281, 84100, 207025, 131044, 298116, 250000, 372100, 280900, 722500, 423801, 722500, 672400, 1102500, 708964, 1690000, 925444, 1863225, 1488400, 2102500, 1690000, 3651921
Offset: 1
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
- Ramanujan's Papers, Some formulas in the analytic theory of numbers, Messenger of Mathematics, XLV, 1916, 81-84, Formula (15), a=b=2.
Programs
-
Mathematica
Table[DivisorSigma[2, n]^2, {n, 1, 40}] -
PARI
a(n) = sigma(n, 2)^2; \\ Michel Marcus, Aug 11 2022
Formula
Dirichlet g.f.: zeta(s) * zeta(s-2)^2 * zeta(s-4) / zeta(2*s-4).
Multiplicative with a(p^e) = ((p^(2*e+2)-1)/(p^2-1))^2. - Amiram Eldar, Aug 11 2022
a(n) = A001157(n)^2. - R. J. Mathar, Aug 18 2022