%I #21 Jul 08 2024 08:52:37

%S 1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,

%T 1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,

%U 1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,0,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1

%N a(n) = 1 if 2*phi(n) > n, otherwise 0, where phi is Euler's totient function phi, A000010.

%H Antti Karttunen, <a href="/A374134/b374134.txt">Table of n, a(n) for n = 1..100000</a>

%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>

%F a(n) = [A083254(n) > 0], where [ ] is the Iverson bracket.

%F a(2*k) = 0 for k >= 1. - _Paolo Xausa_, Jul 08 2024

%t Array[Boole[2*EulerPhi[#] > #] &, 100] (* _Paolo Xausa_, Jul 08 2024 *)

%o (PARI) A374134(n) = ((2*eulerphi(n))>n);

%Y Characteristic function of A089684.

%Y Cf. A000010, A083254, A318874 (inverse Möbius transform), A323170.

%Y Differs from A000035 first at n=105, where a(105) = 0, while A000035(105) = 1.

%Y Differs from A374136 first at n=255, where a(255) = 1, while A374136(255) = 0.

%K nonn

%O 1

%A _Antti Karttunen_, Jul 06 2024