OFFSET
1,2
REFERENCES
S. Ramanujan, Some formulas in the analytic theory of numbers, Mess. Math. 45 (1915), 81-84, eq. 15. (Reprinted in Collected Papers of Srinivasa Ramanujan, Chelsea Publ., New York 1962, 133-135)
LINKS
J. G. Wurtzel, Table of n, a(n) for n=1..10000
FORMULA
Dirichlet g.f.: zeta(s)*zeta(s-1)^2*zeta(s-2)/zeta(2*s-2), Re(s)>3. - Antonio G. Astudillo (afg_astudillo(AT)hotmail.com), Jul 21 2002
From Vladeta Jovovic, Jul 30 2002: (Start)
Multiplicative with a(p^e) = ((p^(e+1)-1)/(p-1))^2.
a(n) = Sum_{d|n} n/d*sigma(d^2). (End)
Equals the Dirichlet convolution of A065764 by A000027: a(n) = sigma(n^2) * n. - R. J. Mathar, Apr 02 2011
Sum_{k>=1} 1/a(k) = A109693 = 1.3064565120389505680107494870912715497583907915664910373609699598615342645... - Vaclav Kotesovec, Sep 20 2020
MATHEMATICA
Table[DivisorSigma[1, n]^2, {n, 1, 50}] (* Vaclav Kotesovec, Feb 05 2019 *)
PROG
(PARI) a(n)=sigma(n)^2; /* Joerg Arndt, Oct 07 2012 */
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
N. J. A. Sloane, Jul 26 2002
STATUS
approved