OFFSET
1,4
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A000203(n) - 2*A000005(n) + 1 = A000203(n) - A114003(n) = A088580(n) - A062011(n). - Omar E. Pol, Sep 30 2017
G.f.: Sum_{k>=1} x^(3*k) / (1 - x^k)^2. - Ilya Gutkovskiy, Apr 24 2021
MATHEMATICA
Table[DivisorSigma[1, n] - 2 DivisorSigma[0, n] + 1, {n, 60}] (* Ivan Neretin, Sep 30 2017 *)
PROG
(PARI) a(n) = sigma(n) - 2*numdiv(n) + 1; \\ Michel Marcus, Sep 30 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Dec 14 2008
STATUS
approved