OFFSET
1,2
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
Joerg Arndt, On computing the generalized Lambert series, arXiv:1202.6525v3 [math.CA], (2012).
FORMULA
G.f.: Sum_{n>=1} n*(n-1) * x^n/(1-x^n). - Joerg Arndt, Jan 30, 2011
L.g.f.: -log(Product_{k>=1} (1 - x^k)^(k-1)) = Sum_{n>=1} a(n)*x^n/n. - Ilya Gutkovskiy, May 21 2018
From Peter Bala, Jan 21 20221; (Start)
a(n) = 2*A069153(n).
G.f.: A(x) = Sum_{n >= 1} 2*x^(2*n)/(1 - x^n)^3.
A faster converging series: A(x) = Sum_{n >= 1} x^(n^2)*( n*(n-1)*x^(3*n) - (n^2 + n - 2)*x^(2*n) + n*(3 - n)*x^n + n*(n - 1) )/(1 - x^n)^3 - differentiate equation 5 in Arndt twice w.r.t x and set x = 1. (End)
MATHEMATICA
Table[DivisorSigma[2, n]-DivisorSigma[1, n], {n, 50}] (* Harvey P. Dale, Aug 01 2020 *)
PROG
(PARI) for (n=2, 50, print1(sigma(n, 2)-sigma(n, 1)", "))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jon Perry, Jul 27 2003
STATUS
approved