OFFSET
1,10
COMMENTS
A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
FORMULA
G.f.: Sum_{k>=1} (-1)^k * x^prime(k) / (1 - x^prime(k)). - Ilya Gutkovskiy, Feb 12 2020
Additive with a(p^e) = (-1)^primepi(p). - Amiram Eldar, Jun 17 2024
MATHEMATICA
Table[Total[(-1)^PrimePi/@First/@If[n==1, {}, FactorInteger[n]]], {n, 100}]
CROSSREFS
KEYWORD
sign
AUTHOR
Gus Wiseman, May 17 2019
STATUS
approved