A237418 Primes of the form 4^k + 15.

19, 31, 79, 271, 1039, 4111, 65551, 4194319, 67108879, 1073741839, 4294967311, 1099511627791, 4398046511119, 70368744177679, 4722366482869645213711, 75557863725914323419151

Offset: 1

Author

Vincenzo Librandi, Feb 22 2014

Keywords

• nonn
• easy

Comments

Subsequence of A144487.

Examples

			65551 is a term because 4^8 + 15 = 65551 is prime.
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..26

Crossrefs

Cf. A000040, A144487, A253773 (corresponding k's).

Programs

Magma

[a: n in [1..70] | IsPrime(a) where a is 4^n+15];

Mathematica

Select[Table[4^n + 15, {n, 1, 200}],PrimeQ]

Formula

a(n) = 4^A253773(n) + 15. - Elmo R. Oliveira, Nov 28 2023