OFFSET
1,2
COMMENTS
It is known that a(n) >= 0.
REFERENCES
József Sándor, Dragoslav S. Mitrinovic, and Borislav Crstici, Handbook of Number Theory I, Springer Science & Business Media, 2005, Chapter III, p. 77, section III.1.1.a.
Wacław Sierpiński, Elementary Theory of Numbers. Państ. Wydaw. Nauk., Warsaw, 1964.
LINKS
Wacław Sierpiński, Elementary Theory of Numbers, Warszawa, 1964.
MATHEMATICA
s[n_] := If[CompositeQ[n], DivisorSigma[1, n] - Ceiling[n + Sqrt[n]], Nothing]; Array[s, 100] (* Amiram Eldar, Apr 25 2024 *)
PROG
(PARI) lista(nn) = forcomposite(n=1, nn, print1(sigma(n) - ceil(n + sqrt(n)), ", ")); \\ Michel Marcus, Dec 12 2014
(Python)
from math import isqrt
from sympy import divisor_sigma, composite
def A079529(n): return divisor_sigma(m:=composite(n))-1-m-isqrt(m-1) # Chai Wah Wu, Jul 29 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 22 2003
STATUS
approved