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
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
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