OFFSET
1,2
COMMENTS
After 1, m is of the form 3*k+2. In fact, for m = 3*k or 3*k+1, 4^n+17 is divisible by 9 and 7, respectively. [Bruno Berselli, Aug 26 2015]
a(21) > 300000. - Robert Price, Apr 04 2017
EXAMPLE
2 is in the sequence because (4^2+17)/3 = 11 is prime.
5 is in the sequence because (4^5+17)/3 = 347 is prime.
MATHEMATICA
Select[Range[0, 5000], PrimeQ[(4^# + 17)/3] &]
PROG
(Magma) [n: n in [0..1000] | IsPrime((4^n+17) div 3)];
(PARI) for(n=1, 1e3, if(isprime((4^n+17)/3), print1(n", "))) \\ Altug Alkan, Sep 14 2015
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, Aug 26 2015
EXTENSIONS
a(14)-a(15) from Vincenzo Librandi, Sep 14 2015
a(16)-a(20) from Robert Price, Feb 01 2017
STATUS
approved