OFFSET
2,4
LINKS
Paolo Xausa, Table of n, a(n) for n = 2..10000
MATHEMATICA
Join[{-1}, Array[MoebiusMu[#] * EulerPhi[#]/2 &, 100, 3]] (* Paolo Xausa, Apr 17 2024 *)
PROG
(PARI) a(n) = if(n<=2, -1, eulerphi(n)/2*moebius(n)); \\ Michel Marcus, Apr 14 2024
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Jason Earls, Jul 22 2001
STATUS
approved