The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A217384 Numbers n such that 9^n + 4 is prime. 4
 0, 1, 3, 5, 11, 15, 21, 87, 99, 281, 497, 2919, 6849, 7365, 8483, 49317, 58611 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Contribution from Bruno Berselli, Oct 04 2012: (Start) Contains exactly the halved even terms of A058958. Naturally, apart from the first term, these numbers are odd since (10-1)^(2n)+4 is divisible by 5. (End) a(18) > 10^5. - Tyler NeSmith, May 05 2021 LINKS MATHEMATICA Select[Range[0, 3000], PrimeQ[9^# + 4] &] PROG (PARI) is(n)=ispseudoprime(9^n+4) \\ Charles R Greathouse IV, Feb 20 2017 CROSSREFS Cf. A058958, A090649. Sequence in context: A105772 A244520 A034169 * A335279 A136977 A003529 Adjacent sequences: A217381 A217382 A217383 * A217385 A217386 A217387 KEYWORD nonn,hard,more AUTHOR Vincenzo Librandi, Oct 04 2012 EXTENSIONS a(13)-a(14) from Bruno Berselli, Oct 04 2012 a(15)-a(17) from Tyler NeSmith, May 05 2021 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified January 29 13:38 EST 2023. Contains 359923 sequences. (Running on oeis4.)