A353681 - OEIS

%I #11 May 06 2022 17:03:35

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

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

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

%N a(n) = 1 if phi(sigma(n)) > phi(n), otherwise 0.

%H Antti Karttunen, <a href="/A353681/b353681.txt">Table of n, a(n) for n = 1..100000</a>

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

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%F a(n) = [A353636(n) > 0], where [ ] is the Iverson bracket.

%F a(n) = A353682(n) - A353637(n).

%t Table[Boole[EulerPhi[DivisorSigma[1, n]] > EulerPhi[n]], {n, 1, 120}] (* _Amiram Eldar_, May 06 2022 *)

%o (PARI) A353681(n) = (eulerphi(sigma(n))>eulerphi(n));

%Y Characteristic function of A353683, while its complement A353685 gives the positions of zeros.

%Y Cf. A000010, A000203, A062401, A353636, A353637, A353682.

%K nonn

%O 1

%A _Antti Karttunen_, May 06 2022