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A228076 Numbers k such that (19^k - 4^k)/15 is prime. 0
2, 7, 11, 31, 47, 139, 263, 769, 20551, 21491, 112247 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are prime.

a(12) > 2*10^5.

LINKS

Table of n, a(n) for n=1..11.

MATHEMATICA

Select[Prime[Range[1, 100000]], PrimeQ[(19^# - 4^#)/15]&]

PROG

(PARI) is(n)=ispseudoprime((19^n-4^n)/15) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A224691, A128354, A128032.

Sequence in context: A327552 A336342 A284354 * A123151 A026133 A026162

Adjacent sequences:  A228073 A228074 A228075 * A228077 A228078 A228079

KEYWORD

nonn,hard,more

AUTHOR

Robert Price, Aug 09 2013

EXTENSIONS

a(11) from Robert Price, Mar 06 2021

STATUS

approved

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Last modified September 27 13:12 EDT 2022. Contains 357062 sequences. (Running on oeis4.)