A152772 a(n) = sigma(n) - 3*d(n) + 3.

1, 0, 1, 1, 3, 3, 5, 6, 7, 9, 9, 13, 11, 15, 15, 19, 15, 24, 17, 27, 23, 27, 21, 39, 25, 33, 31, 41, 27, 51, 29, 48, 39, 45, 39, 67, 35, 51, 47, 69, 39, 75, 41, 69, 63, 63, 45, 97, 51, 78, 63, 83, 51, 99, 63, 99, 71, 81, 57, 135

Offset: 1

Author

Omar E. Pol, Dec 14 2008

Keywords

• easy
• nonn

Crossrefs

Cf. A000005 (d), A000203 (sigma), A152770, A152771.

Programs

Mathematica

a[n_] := DivisorSigma[1, n] - 3 * DivisorSigma[0, n] + 3; Array[a, 100] (* Amiram Eldar, Apr 07 2024 *)

PARI

a(n) = sigma(n) - 3 * numdiv(n) + 3; \\ Amiram Eldar, Apr 07 2024