A323170 a(n) = 1 if (2*phi(n)) < n, 0 otherwise, where phi is Euler totient function (A000010).

0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 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, 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, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1

Offset

1

Comments

Characteristic function of A054741.

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Mitsuo Kobayashi, A generalization of a series for the density of abundant numbers, International Journal of Number Theory, Vol. 12, No. 3 (2016), pp. 671-677.

Index entries for characteristic functions.

Formula

Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) is in the range (0.51120, 0.51176) (Kobayashi, 2016). - Amiram Eldar, Jun 01 2025

Mathematica

Array[Boole[2*EulerPhi[#] < #] &, 100] (* Paolo Xausa, Jul 08 2024 *)

Prog

(PARI) A323170(n) = ((2*eulerphi(n))<n);

Crossrefs

Cf. A000010, A054741, A083254, A318875 (Inverse Möbius transform), A374134.

Sequence in context: A363915 A353671 A353672 * A379118 A215480 A143731

Adjacent sequences: A323167 A323168 A323169 * A323171 A323172 A323173

Keyword

nonn

Author

Antti Karttunen, Jan 05 2019

Status

approved