A171405 Sum of divisors of n, excluding divisors 2 and 3.

1, 1, 1, 5, 6, 7, 8, 13, 10, 16, 12, 23, 14, 22, 21, 29, 18, 34, 20, 40, 29, 34, 24, 55, 31, 40, 37, 54, 30, 67, 32, 61, 45, 52, 48, 86, 38, 58, 53, 88, 42, 91, 44, 82, 75, 70, 48, 119, 57, 91, 69, 96, 54, 115, 72, 118, 77, 88, 60, 163, 62, 94, 101, 125, 84, 139, 68, 124, 93, 142

Offset: 1

Author

Juri-Stepan Gerasimov, Dec 07 2009, Apr 20 2010

Keywords

• nonn

Crossrefs

Cf. A000203, A178142.

Programs

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 *)

PARI

a(n) = sigma(n) - [0,2,3,2,0,5][(n-1) % 6 + 1]; \\ Amiram Eldar, Aug 03 2024

Formula

a(n) = A000203(n) - A178142(n). - Amiram Eldar, Aug 03 2024

Extensions

Definition and some values corrected by R. J. Mathar, Jun 07 2010