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A215487 Numbers n such that (7^n - 2^n)/5 is prime. 1
3, 7, 19, 79, 431, 1373, 1801, 2897, 46997 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are prime.

a(10) > 10^5.

LINKS

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

MATHEMATICA

Select[ Prime[ Range[1, 100000] ], PrimeQ[ ((7^# - 2^#)/5 ]& ]

PROG

(PARI) is(n)=ispseudoprime((7^n-2^n)/5) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.

Sequence in context: A217611 A322852 A243583 * A146037 A172514 A128024

Adjacent sequences:  A215484 A215485 A215486 * A215488 A215489 A215490

KEYWORD

hard,more,nonn

AUTHOR

Robert Price, Aug 12 2012

STATUS

approved

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Last modified May 26 17:17 EDT 2019. Contains 323597 sequences. (Running on oeis4.)