%I #25 Oct 28 2024 04:51:32
%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);
%o (Python)
%o from sympy import totient
%o def A374134(n): return int(totient(n)<<1>n) # _Chai Wah Wu_, Oct 27 2024
%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