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A213073 Numbers n such that (7^n - 4^n)/3 is prime. 1
2, 5, 11, 61, 619, 2879, 2957, 24371, 69247 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are primes.

Next term > 10^5.

LINKS

Table of n, a(n) for n=1..9.

MATHEMATICA

k=7; Do[p=Prime[n]; f=(k^p-4^p)/(k-4); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]

PROG

(PARI) is(n)=ispseudoprime((7^n-4^n)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A128344, A128024, A059802.

Sequence in context: A140547 A131480 A262228 * A267527 A286453 A018847

Adjacent sequences:  A213070 A213071 A213072 * A213074 A213075 A213076

KEYWORD

hard,more,nonn

AUTHOR

Robert Price, Jun 04 2012

STATUS

approved

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Last modified October 22 20:57 EDT 2018. Contains 316502 sequences. (Running on oeis4.)