cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A387197 Numbers k such that 32 * 3^k - 1 is prime.

Original entry on oeis.org

0, 3, 4, 6, 46, 59, 84, 94, 124, 239, 267, 366, 371, 424, 616, 2139, 2299, 3523, 3563, 3843, 3923, 7627, 12751, 34798, 39911, 56568, 58779
Offset: 1

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Author

Ken Clements, Aug 21 2025

Keywords

Comments

a(28) > 10^5.
Conjecture: This sequence intersects with A387201 at k = 4 to form twin primes with center N = 2^5 * 3^4 = 2592 = A027856(10). Any such intersection has to be at an even k because if k is odd, either N-1 or N+1 has to be divisible by 5. A covering system can be constructed that eliminates all other intersections except where k = 4(mod 60), and for k > 4 with k = 4(mod 60), the search up to 10^5 makes the probability of another intersection in this residue class vanishingly small.

Crossrefs

Programs

  • Mathematica
    Select[Range[0, 4000], PrimeQ[32 * 3^# - 1] &] (* Amiram Eldar, Aug 21 2025 *)
  • Python
    from gmpy2 import is_prime
    print([ k for k in range(4000) if is_prime(32 * 3**k - 1)])
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