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 A046867 Numbers n such that 10*11^n -1 is prime. 15
 1, 3, 37, 119, 255, 355, 371, 497, 1759, 34863, 50719, 147709 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(13) > 2*10^5. - Robert Price, Jan 19 2015 REFERENCES R. K. Guy, Unsolved Problems in Theory of Numbers, Section A3. LINKS H. C. Williams, The primality of certain integers of the form 2Ar^n - 1, Acta Arith. 39 (1981), 7-17. MATHEMATICA Do[ If[ PrimeQ[10*11^n - 1], Print[n]], {n, 1, 2000}] PROG (PARI) is(n)=isprime(10*11^n-1) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A003307, A002235, A046865, A079906, A046866, A001771, A005541, A056725, A079907. Sequence in context: A301358 A163156 A041067 * A154823 A109835 A066364 Adjacent sequences:  A046864 A046865 A046866 * A046868 A046869 A046870 KEYWORD nonn,hard AUTHOR EXTENSIONS One more term from Robert G. Wilson v, Jan 16 2003 a(10)-a(12) from Robert Price, Jan 19 2015 STATUS approved

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Last modified October 19 13:01 EDT 2019. Contains 328222 sequences. (Running on oeis4.)