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 A125956 Numbers k such that (2^k + 9^k)/11 is prime. 6
 3, 7, 127, 283, 883, 1523, 4001 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are primes. Note that first 3 terms (3, 7, 127} are primes of the form 2^q - 1, where q = {2, 3, 7) is prime too. Corresponding primes of the form (2^n + 9^n)/11 are {67, 434827, ...}. a(8) > 10^5. - Robert Price, Dec 23 2012 LINKS MATHEMATICA Do[p=Prime[n]; f=(2^p+9^p)/11; If[PrimeQ[f], Print[{p, f}]], {n, 1, 100}] PROG (PARI) is(n)=ispseudoprime((2^n+9^n)/11) \\ Charles R Greathouse IV, Feb 20 2017 CROSSREFS Cf. A000978 = numbers n such that (2^n + 1)/3 is prime. Cf. A057469 = numbers n such that (2^n + 3^n)/5 is prime. Cf. A082387 = numbers n such that (2^n + 5^n)/7 is prime. Sequence in context: A066771 A139159 A042329 * A260642 A128071 A079622 Adjacent sequences:  A125953 A125954 A125955 * A125957 A125958 A125959 KEYWORD hard,more,nonn AUTHOR Alexander Adamchuk, Feb 06 2007 EXTENSIONS 2 more terms from Rick L. Shepherd, Feb 14 2007 a(7) from Robert Price, Dec 23 2012 STATUS approved

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Last modified May 19 20:41 EDT 2019. Contains 323410 sequences. (Running on oeis4.)