A138578 Numbers k such that 2^(2*k-7)-7 is prime.

23, 361, 995, 1163, 1253, 1891, 6413, 31795, 60781, 60923

Offset

1,1

Links

Table of n, a(n) for n=1..10.

Example

2^(2*23-7) - 7 = 549755813881 is prime.

Prog

(PARI) is(n)=isprime(2^(2*n-7)-7) \\ Charles R Greathouse IV, Jun 13 2017
(Python)
from sympy import isprime
def afind(limit):
  k = 5; pow2 = 2**(2*k-7)
  while k < limit:
    while not isprime(pow2 - 7) and k <= limit: k += 1; pow2 *= 4
    if k > limit: return
    print(k, end=", "); k += 1; pow2 *= 4
afind(2000) # Michael S. Branicky, Apr 23 2021

Crossrefs

Sequence in context: A025964 A180361 A021684 * A077515 A025942 A020000

Adjacent sequences: A138575 A138576 A138577 * A138579 A138580 A138581

Keyword

nonn,more

Author

Vladimir Joseph Stephan Orlovsky, May 13 2008

Extensions

a(6)-a(7) from Michael S. Branicky, Apr 23 2021

a(8)-a(10) from Michael S. Branicky, Sep 12 2024

Status

approved