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A217384
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Numbers n such that 9^n + 4 is prime.
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4
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0, 1, 3, 5, 11, 15, 21, 87, 99, 281, 497, 2919, 6849, 7365, 8483, 49317, 58611
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OFFSET
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1,3
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COMMENTS
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Contribution from Bruno Berselli, Oct 04 2012: (Start)
Contains exactly the halved even terms of A058958.
Naturally, apart from the first term, these numbers are odd since (10-1)^(2n)+4 is divisible by 5. (End)
a(18) > 10^5. - Tyler NeSmith, May 05 2021
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LINKS
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Table of n, a(n) for n=1..17.
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MATHEMATICA
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Select[Range[0, 3000], PrimeQ[9^# + 4] &]
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PROG
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(PARI) is(n)=ispseudoprime(9^n+4) \\ Charles R Greathouse IV, Feb 20 2017
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CROSSREFS
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Cf. A058958, A090649.
Sequence in context: A105772 A244520 A034169 * A335279 A136977 A003529
Adjacent sequences: A217381 A217382 A217383 * A217385 A217386 A217387
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KEYWORD
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nonn,hard,more
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AUTHOR
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Vincenzo Librandi, Oct 04 2012
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EXTENSIONS
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a(13)-a(14) from Bruno Berselli, Oct 04 2012
a(15)-a(17) from Tyler NeSmith, May 05 2021
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STATUS
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approved
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