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A219039
Numbers k such that 3^k - 16 is prime.
16
3, 5, 11, 15, 51, 69, 99, 227, 381, 537, 9135, 9737, 58437, 105567, 121779, 123645
OFFSET
1,1
COMMENTS
a(17) > 2*10^5. - Robert Price, Sep 29 2013
EXAMPLE
For k = 3, 3^3 - 16 = 11 and 11 is prime. Hence k = 3 is included in the sequence.
MATHEMATICA
Do[If[PrimeQ[3^n - 16], Print[n]], {n, 1, 10000}]
PROG
(PARI) is(n)=isprime(3^n-16) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
Cf. Sequences of numbers k such that 3^k + m is prime:
(m = 2) A051783, (m = -2) A014224, (m = 4) A058958, (m = -4) A058959,
(m = 8) A217136, (m = -8) A217135, (m = 10) A217137, (m = -10) A217347,
(m = 14) A219035, (m = -14) A219038, (m = 16) A205647, (m = -16) this sequence, (m = 20) A219040, (m = -20) A219041.
Note that if m is a multiple of 3, 3^k + m is also a multiple of 3 (for k greater than 0), and as such isn't prime.
Sequence in context: A318915 A322439 A018313 * A074820 A327043 A006169
KEYWORD
nonn,more
AUTHOR
Nicolas M. Perrault, Nov 10 2012
EXTENSIONS
a(13)-a(16) from Robert Price, Sep 29 2013
STATUS
approved