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 A172995 Numbers n such that (3^n+7)/2 is prime. 1
 1, 3, 7, 75, 191, 395, 891, 2935, 3855 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The primes are in A172996. The next term are > 10000. Vincenzo Librandi, Oct 05 2012 Naturally these numbers are odd since 3^(2n)+7 = (8+1)^n+7 == 0 (mod 8). - Bruno Berselli, Oct 08 2012 LINKS MATHEMATICA Select[Range[5000], PrimeQ[(3^# + 7) / 2 ]&] (* Vincenzo Librandi, Oct 05 2012 *) PROG (PARI) is(n)=ispseudoprime((3^n+7)/2) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Sequence in context: A075611 A191485 A119572 * A325476 A234536 A103737 Adjacent sequences:  A172992 A172993 A172994 * A172996 A172997 A172998 KEYWORD nonn,hard,more AUTHOR Vincenzo Librandi, Feb 07 2010 EXTENSIONS a(7)-(9) from Vincenzo Librandi, Oct 05 2012 STATUS approved

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Last modified September 19 18:37 EDT 2020. Contains 337181 sequences. (Running on oeis4.)