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A059613 Numbers k such that 5^k - 4 is prime. 8
5, 7, 15, 47, 81, 115, 267, 285, 7641, 19089, 25831, 32115, 59811, 70155, 178715 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
a(15) > 10^5. - Robert Price, Feb 03 2014
a(16) > 2*10^5. - Tyler NeSmith, Jul 25 2021
LINKS
EXAMPLE
81 is present because 5^81 - 4 is prime.
MATHEMATICA
Select[Range[10000], PrimeQ[5^# - 4] &] (* Vincenzo Librandi, Oct 03 2012 *)
PROG
(PARI) is(n)=ispseudoprime(5^n-4) \\ Charles R Greathouse IV, Feb 20 2017
CROSSREFS
Cf. A164785.
Sequence in context: A076860 A283592 A067589 * A242503 A116048 A120282
KEYWORD
nonn,hard,more
AUTHOR
Andrey V. Kulsha, Feb 07 2001
EXTENSIONS
a(10)-a(14) from Robert Price, Feb 03 2014
a(15) from Tyler NeSmith, Jul 25 2021
STATUS
approved

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Last modified April 22 00:17 EDT 2024. Contains 371886 sequences. (Running on oeis4.)