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A128344 Numbers n such that (7^n - 5^n)/2 is prime. 18
3, 5, 7, 113, 397, 577 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

COMMENTS

All terms are primes.

MATHEMATICA

k=7; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]

CROSSREFS

Cf. A062572, A128345, A128346, 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: A110337 A132287 A046201 * A114366 A088092 A174271

Adjacent sequences:  A128341 A128342 A128343 * A128345 A128346 A128347

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk (alex(AT)kolmogorov.com), Feb 27 2007

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Last modified February 16 17:48 EST 2012. Contains 205939 sequences.