A089213 Primes p such that either 3^p-2 or 3^p+2 is prime.

2, 3, 5, 37, 41, 139, 317, 541, 2521

Offset

1,1

Comments

At p = 2, 3, 139, 3^p + 2 is prime, while at p = 2, 5, 37, 41, 317, 541, 2521 3^p - 2 is prime.

a(10) > 2*10^5. - Robert Price, Nov 20 2013

Links

Table of n, a(n) for n=1..9.

Example

2 is in the sequence because both 3^2 - 2 = 7 and 3^2 + 2 = 11 are primes.
3 is in the sequence because 3^3 + 2 = 29 is a prime (though 3^3 - 2 = 25 = 5^2).
5 is in the sequence because 3^5 - 2 = 241 is a prime (though 3^5 + 2 = 245 = 5 * 7^2).

Mathematica

Select[Prime[Range[100]], PrimeQ[3^# - 2] || PrimeQ[3^# + 2] &] (* Alonso del Arte, Nov 20 2013 *)

Crossrefs

Cf. A014224, A051783.

Sequence in context: A362640 A261130 A271387 * A029499 A347720 A128026

Adjacent sequences: A089210 A089211 A089212 * A089214 A089215 A089216

Keyword

nonn,more,hard

Author

Herman H. Rosenfeld (herm3(AT)pacbell.net), Dec 20 2003

Extensions

Edited by Zak Seidov, Aug 08 2006

Status

approved