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A125956
Numbers k such that (2^k + 9^k)/11 is prime.
7
3, 7, 127, 283, 883, 1523, 4001
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^k + 9^k)/11 are {67, 434827, ...}.
a(8) > 10^5. - Robert Price, Dec 23 2012
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
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