A322952 Numbers k such that 321*2^k+1 is prime.

1, 5, 32, 68, 109, 128, 133, 212, 241, 653, 776, 1339, 1787, 2659, 6388, 6547, 8365, 16699, 62861, 64795, 83227, 195376, 278875, 442480, 542876, 730321, 1168576, 1257859, 1629307, 4715725

Offset: 1

Author

Robert Price, Dec 31 2018

Keywords

• nonn
• more
• hard

Links

• Ray Ballinger, Proth Search Page
• Ray Ballinger and Wilfrid Keller, List of primes k.2^n + 1 for 300 < k < 600
• Y. Gallot, Proth.exe: Windows Program for Finding Large Primes
• Wilfrid Keller, List of primes k.2^n - 1 for k < 300
• Eric Weisstein's World of Mathematics, Proth Prime
• Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

Crossrefs

Cf. A002255, A050527.

Programs

Maple

select(n->isprime(321*2^n+1),[$1..1000]); # Muniru A Asiru, Dec 31 2018

Mathematica

Select[Range[1000], PrimeQ[321*2^# + 1] &] (* Robert Price, Dec 31 2018 *)

Extensions

a(30) from Jeppe Stig Nielsen, Dec 20 2024