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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

Table of n, a(n) for n=1..9.

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.)