OFFSET
1,2
LINKS
D. B. Lahiri, Some arithmetical identities for Ramanujan's and divisor functions, Bulletin of the Australian Mathematical Society, Volume 1, Issue 3 December 1969, pp. 307-314. See Theorem 1 p. 308.
FORMULA
G.f.: Sum_{k>=2} (k^2 - 1) * x^k / (1 - x^k)^2. - Ilya Gutkovskiy, Apr 15 2020
MATHEMATICA
a[n_] := (n - 1) * DivisorSigma[1, n]; Array[a, 50] (* Amiram Eldar, Apr 15 2020 *)
PROG
(PARI) a(n) = (n-1)*sigma(n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Apr 15 2020
STATUS
approved