A393387 Numbers k such that 39*2^k + 5 is prime.

1, 3, 9, 15, 18, 31, 34, 37, 51, 73, 78, 216, 219, 304, 318, 342, 712, 834, 1095, 1171, 1368, 1642, 1845, 2179, 3502, 3595, 3762, 3861, 6717, 9135, 9624, 10171, 11161, 15399, 22099, 23056, 33424, 34602, 37654, 47854, 48843, 51423, 64216, 67533, 68463, 86557, 104241

Offset

1,2

Links

Table of n, a(n) for n=1..47.

Example

9 is in this sequence because 39*2^9 + 5 = 19973 is prime.
Initial terms and associated primes:
  a(1) = 1, 83;
  a(2) = 3, 317;
  a(3) = 9, 19973;
  a(4) = 15, 1277957;
  a(5) = 18, 10223621;
  a(6) = 31, 83751862277, etc.

Prog

(PARI) is(k) = ispseudoprime(39*2^k + 5)

Crossrefs

Cf. A002269.

Sequence in context: A071123 A298014 A071347 * A093414 A123998 A117105

Adjacent sequences: A393384 A393385 A393386 * A393388 A393389 A393390

Keyword

nonn

Author

Zhicheng Wei, Feb 13 2026

Extensions

a(35) onward from Michael S. Branicky, Feb 14 2026

Status

approved