A240173 - OEIS

%I #29 Oct 03 2024 03:50:14

%S 1,2,13,43,45,51,53,55,57,63,72,77,81,84,85,89,93,103,108,117,121,129,

%T 147,149,151,163,171,173,177,183,191,213,229,231,239,241,250,259,261,

%U 263,273,283,286,291,321,331,333,344,345,351,353,361,373,381,390,399

%N Numbers n such that k^n - 2^k is not prime for any k.

%C Numbers n such that A245459(n) = 0.

%H Amiram Eldar, <a href="/A240173/b240173.txt">Table of n, a(n) for n = 1..64</a>

%F A245459(a(n)) = 0.

%o (Python)

%o import sympy

%o def a(n):

%o   k = 2

%o   count = 0

%o   while k**n > 2**k:

%o     if sympy.isprime(k**n-2**k):

%o       count += 1

%o     k += 1

%o   return count

%o n = 1

%o while n < 1000:

%o   if not a(n):

%o     print(n, end=', ')

%o   n += 1 # _Derek Orr_, Aug 02 2014

%Y Cf. A245459.

%K nonn

%O 1,2

%A _Juri-Stepan Gerasimov_, Aug 02 2014

%E a(13)-a(34) from _Derek Orr_, Aug 02 2014

%E a(35) onwards from _Amiram Eldar_, Oct 03 2024