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A128335 Numbers n such that (4^n + 5^n)/9 is prime. 31
5, 7, 19, 29, 61, 137, 883, 1381, 1823, 5227, 25561, 29537, 300893 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are primes.

LINKS

Table of n, a(n) for n=1..13.

Top probable primes of the form (5^p+4^p)/9

MATHEMATICA

k=4; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]

PROG

(PARI) forprime(p=3, 1e4, if(ispseudoprime((5^p+4^p)/9), print1(p", "))) \\ Charles R Greathouse IV, Jul 16, 2011

CROSSREFS

Sequence in context: A255490 A045446 A106074 * A023246 A022889 A001562

Adjacent sequences:  A128332 A128333 A128334 * A128336 A128337 A128338

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Feb 27 2007

EXTENSIONS

3 more terms from Ryan Propper, Feb 06 2008

Two more terms from Ryan Propper, May 02 2010

New term 300893 found by Jean-Louis Charton in November 2011 corresponding to a probable prime with 210315 digits.

STATUS

approved

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Last modified May 20 12:33 EDT 2019. Contains 323422 sequences. (Running on oeis4.)