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A128346 Numbers n such that (9^n - 5^n)/4 is prime. 20
3, 11, 17, 173, 839, 971, 40867, 45821 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are primes.

a(9) > 10^5. - Robert Price, Jan 19 2013

LINKS

Table of n, a(n) for n=1..8.

MATHEMATICA

k=9; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]

PROG

(PARI) is(n)=isprime((9^n-5^n)/4) \\ Charles R Greathouse IV, Feb 17 2017

CROSSREFS

Cf. A062572, A128344, A128345, A128347, A128348, A128349, A128350, A128351, A128352, A128353, A128354. Cf. A004061, A082182, A121877, A059802. Cf. A057171, A082387, A122853, A128335, A128336, A128337, A128338, A128339, A128340, A128341, A128342.

Sequence in context: A124787 A080306 A036448 * A128031 A194128 A127995

Adjacent sequences:  A128343 A128344 A128345 * A128347 A128348 A128349

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Feb 27 2007

EXTENSIONS

a(7)-a(8) from Robert Price, Jan 19 2013

a(8) corrected by Robert Price, Jan 20 2013

STATUS

approved

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Last modified May 19 20:41 EDT 2019. Contains 323410 sequences. (Running on oeis4.)