A240173 Numbers n such that k^n - 2^k is not prime for any k.

1, 2, 13, 43, 45, 51, 53, 55, 57, 63, 72, 77, 81, 84, 85, 89, 93, 103, 108, 117, 121, 129, 147, 149, 151, 163, 171, 173, 177, 183, 191, 213, 229, 231, 239, 241, 250, 259, 261, 263, 273, 283, 286, 291, 321, 331, 333, 344, 345, 351, 353, 361, 373, 381, 390, 399

Offset

1,2

Comments

Numbers n such that A245459(n) = 0.

Links

Amiram Eldar, Table of n, a(n) for n = 1..64

Formula

A245459(a(n)) = 0.

Prog

(Python)
import sympy
def a(n):
  k = 2
  count = 0
  while k**n > 2**k:
    if sympy.isprime(k**n-2**k):
      count += 1
    k += 1
  return count
n = 1
while n < 1000:
  if not a(n):
    print(n, end=', ')
  n += 1 # Derek Orr, Aug 02 2014

Crossrefs

Cf. A245459.

Sequence in context: A138089 A296197 A026594 * A235469 A248198 A102296

Adjacent sequences: A240170 A240171 A240172 * A240174 A240175 A240176

Keyword

nonn

Author

Juri-Stepan Gerasimov, Aug 02 2014

Extensions

a(13)-a(34) from Derek Orr, Aug 02 2014

a(35) onwards from Amiram Eldar, Oct 03 2024

Status

approved