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 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 (list; graph; refs; listen; history; text; internal format)
 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 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

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Last modified April 21 08:49 EDT 2021. Contains 343148 sequences. (Running on oeis4.)