OFFSET
1,4
FORMULA
MATHEMATICA
a[n_] := DivisorSigma[1, n] - {0, 2, 3, 2, 0, 5}[[Mod[n-1, 6] + 1]]; Array[a, 100] (* Amiram Eldar, Aug 03 2024 *)
PROG
(PARI) a(n) = sigma(n) - [0, 2, 3, 2, 0, 5][(n-1) % 6 + 1]; \\ Amiram Eldar, Aug 03 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Dec 07 2009, Apr 20 2010.
EXTENSIONS
Definition and some values corrected by R. J. Mathar, Jun 07 2010
STATUS
approved