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

1,1

COMMENTS

All terms are prime.

a(11) > 10^5.

LINKS

Table of n, a(n) for n=1..10.

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: A057025 A055469 A284354 * A123151 A026133 A026162

Adjacent sequences:  A228073 A228074 A228075 * A228077 A228078 A228079

KEYWORD

nonn,hard,more

AUTHOR

Robert Price, Aug 09 2013

STATUS

approved

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Last modified January 18 11:33 EST 2019. Contains 319271 sequences. (Running on oeis4.)