OFFSET
1,5
MATHEMATICA
a[n_] := DivisorSigma[1, n] - 3 * DivisorSigma[0, n] + 3; Array[a, 100] (* Amiram Eldar, Apr 07 2024 *)
PROG
(PARI) a(n) = sigma(n) - 3 * numdiv(n) + 3; \\ Amiram Eldar, Apr 07 2024
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Omar E. Pol, Dec 14 2008
STATUS
approved