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 A082182 Numbers k such that (5^k - 2^k)/3 is prime. 21
 2, 5, 7, 13, 19, 37, 59, 67, 79, 307, 331, 599, 1301, 12263, 12589, 18443, 20149, 27983 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS No other terms less than 100000. - Robert Price, Apr 06 2012 All terms are primes. Some of the results were computed using the PrimeFormGW (PFGW) primality-testing program. - Hugo Pfoertner, Nov 14 2019 LINKS EXAMPLE Example: a(1)=2 because (5^2 - 2^2)/3 = (25 - 4)/3 = 7 is a prime. MATHEMATICA a={}; Do[p=(5^n-2^n)/3; If[PrimeQ[p], AppendTo[a, n]], {n, 20^2}]; Print[a]; (* Vladimir Joseph Stephan Orlovsky, Apr 29 2008 *) PROG (PARI) forprime(p=2, 1e4, if(ispseudoprime((5^p-2^p)/3), print1(p", "))) \\ Charles R Greathouse IV, Jul 16, 2011 CROSSREFS Sequence in context: A175075 A262392 A056985 * A032719 A275287 A261581 Adjacent sequences:  A082179 A082180 A082181 * A082183 A082184 A082185 KEYWORD more,nonn AUTHOR Hugo Pfoertner, May 22 2003, Jun 23 2003 EXTENSIONS 20149 from Herman Jamke (hermanjamke(AT)fastmail.fm), May 03 2007 27983 from David Radcliffe, May 28 2007 STATUS approved

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Last modified January 22 22:16 EST 2020. Contains 331166 sequences. (Running on oeis4.)