A134753 Numbers n such that 3^(2*n-1) + 2 is prime.

1, 2, 8, 32, 62, 70, 118, 122, 158, 182, 196, 566, 752, 3602, 21896, 22768, 53072

Offset

1,2

Comments

From _Enrique Pérez Herrero_, Jul 29 2010: (Start)

With: f(n)=3^(2n-1)+2, the non-primality of f(n) is settled when:

if 2 does not divide n, 5 divides f(n) (n>1)

if 3 divides n, 7 divides f(n)

if 5 divides n-4, 11 divides f(n)

if 14 divides n-2, 29 divides f(n)

if 15 divides n-5, 31 divides f(n).

(End)

References

_Luis H. Gallardo_, Posting to the Number Theory List, Jan 14 2008

Links

Table of n, a(n) for n=1..17.

L. H. Gallardo, On a remark of Makowski about perfect numbers, El. Mathem. 65 (3) (2010) 121-126

Henri & Renaud Lifchitz, PRP Records.

Formula

({odd terms in A051783} + 1)/2.

Mathematica

Contribution from _Enrique Pérez Herrero_, Jul 29 2010: (Start)
MaxVal = 1000;
dataA134753=Select[Select[Range[MaxVal], #<3||Mod[#, 2]==0&&Mod[#, 3]!=0&&Mod[#, 5]!=4&&Mod[#, 14]!=2&&Mod[#, 15]!=5&], PrimeQ[3^(2*#-1)+2]&]
A134753[n_Integer] := dataA134753[[n]] /; (n > 0 && n <= Length[dataA134753])
(End)

Prog

(PARI) is(n)=isprime(3^(2*n-1)+2) \\ _Charles R Greathouse IV_, Jun 06 2017

Crossrefs

Cf. A051783, A134752.

Sequence in context: A269818 A331823 A006552 * A212892 A302936 A227971

Adjacent sequences: A134750 A134751 A134752 * A134754 A134755 A134756

Keyword

nonn,easy

Author

_N. J. A. Sloane_, Jan 28 2008

Extensions

Typo in prime search corrected _Enrique Pérez Herrero_, Jul 31 2010

a(15)-a(17) from A051783 by _Ray Chandler_, Aug 06 2011

Status

approved