OFFSET
1,4
COMMENTS
Always >= 0 for n >= 2. a(n)=0 if and only if n is prime.
If n is an even semiprime > 4 (A100484), then a(n) = n. - Wesley Ivan Hurt, Dec 25 2013
REFERENCES
József Sándor, Dragoslav S. Mitrinovic, and Borislav Crstici, Handbook of Number Theory I, Springer Science & Business Media, 2005, Chapter I, p. 10, section I.3.1.a (but they have "tau" instead of "sigma").
LINKS
T. D. Noe, Table of n, a(n) for n = 1..10000
N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98).
MAPLE
with(numtheory); A046520:=n->sigma(n)-phi(n)-tau(n); seq(A046520(n), n=1..100); # Wesley Ivan Hurt, Dec 25 2013
MATHEMATICA
DivisorSigma[1, #] - EulerPhi[#] - DivisorSigma[0, #] & /@ Range[74] (* Jayanta Basu, Jun 27 2013 *)
PROG
(PARI) a(n) = {my(f = factor(n)); sigma(f) - eulerphi(f) - numdiv(f); } \\ Amiram Eldar, Apr 25 2024
CROSSREFS
KEYWORD
sign,easy
AUTHOR
EXTENSIONS
Corrected by Dean Hickerson, Dec 19 2006
STATUS
approved