A288654 a(n) = (sigma(n)-n-1)*(3-omega(n)).

-3, 0, 0, 4, 0, 5, 0, 12, 6, 7, 0, 15, 0, 9, 8, 28, 0, 20, 0, 21, 10, 13, 0, 35, 10, 15, 24, 27, 0, 0, 0, 60, 14, 19, 12, 54, 0, 21, 16, 49, 0, 0, 0, 39, 32, 25, 0, 75, 14, 42, 20, 45, 0, 65, 16, 63, 22, 31, 0, 0, 0, 33, 40, 124, 18, 0, 0, 57, 26, 0, 0, 122

Offset: 1

Author

Wesley Ivan Hurt, Jun 12 2017

Keywords

• sign
• easy

Comments

If n is prime, then a(n) = 0. If n is semiprime, then a(n) = sopfr(n).

Links

• Antti Karttunen, Table of n, a(n) for n = 1..65537

Crossrefs

Cf. A000203 (sigma), A001221 (omega), A001414 (sopfr), A048050 (Chowla's function).

Programs

Mathematica

Table[(DivisorSigma[1, n] - n - 1) (3 - PrimeNu[n]), {n, 100}]

PARI

A288654(n) = ((sigma(n)-n-1)*(3-omega(n))); \\ Antti Karttunen, Mar 04 2018