

A261578


Numbers m such that (4^m + 17) / 3 is prime.


1



1, 2, 5, 8, 11, 23, 26, 59, 83, 89, 116, 1103, 1568, 5768, 13376, 17810, 18614, 66209, 167933, 188318
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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


LINKS

Table of n, a(n) for n=1..20.


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

Cf. similar sequences listed in A261539.
Sequence in context: A129300 A107679 A018846 * A264613 A285293 A246442
Adjacent sequences: A261575 A261576 A261577 * A261579 A261580 A261581


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



