A144231 Prime numbers of the form 3^k +- 2 for k >= 1.

5, 7, 11, 29, 79, 83, 241, 727, 6563, 19681, 59051, 4782971, 14348909, 31381059607, 282429536483, 2541865828331, 150094635296999123, 450283905890997361, 36472996377170786401, 1144561273430837494885949696429

Offset: 1

Author

Reikku Kulon, Sep 15 2008

Keywords

• nonn

Comments

a(49) = 3^2224 - 2 and a(50) = 3^2521 - 2 are too big for a b-file. - Robert Israel, Nov 22 2015

Links

• Robert Israel, Table of n, a(n) for n = 1..48

Crossrefs

Cf. A000040, A000668, A014232, A057735.

Programs

Maple

A:= NULL:
for k from 1 to 1000 do
  t:= 3^k;
  if isprime(t-2) then A:= A, t-2 fi;
  if isprime(t+2) then A:= A, t+2 fi;
od:
A; # Robert Israel, Nov 22 2015

Mathematica

Reap[For[k = 1, k <= 100, k++, p = 3^k-2; If[PrimeQ[p], Sow[p]]; If[PrimeQ[p+4], Sow[p+4]]]][[2, 1]] (* Jean-François Alcover, Dec 18 2013 *)