OFFSET
1,2
LINKS
T. D. Noe, Table of n, a(n) for n = 1..10000
FORMULA
G.f.: -1 - 1/x + (1 - x)^2*Sum_{k>=1} k*x^(k-2)/(1 - x^k). - Ilya Gutkovskiy, Jan 29 2017
MATHEMATICA
Table[DivisorSigma[1, n+2] - 2*DivisorSigma[1, n+1] + DivisorSigma[1, n], {n, 1, 100}] (* G. C. Greubel, Sep 03 2018 *)
PROG
(PARI) a(n)=sigma(n+2)-2*sigma(n+1)+sigma(n) \\ Charles R Greathouse IV, Mar 09 2014
(Magma) [DivisorSigma(1, n+2) - 2*DivisorSigma(1, n+1) + DivisorSigma(1, n): n in [1..100]]; // G. C. Greubel, Sep 03 2018
CROSSREFS
KEYWORD
sign
AUTHOR
Asher Auel, Jan 06 2000
STATUS
approved