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A180745 Numbers k such that 7^k - 5^k + 1 is prime. 0
1, 4, 8, 140 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

No further terms k <= 5000. - Harvey P. Dale, Jan 25 2011

No further terms k <= 10000. - Tyler NeSmith, May 06 2021

No further terms k <= 20000. - Jon E. Schoenfield, May 07 2021

LINKS

Table of n, a(n) for n=1..4.

MATHEMATICA

Select[Range[5000], PrimeQ[7^#-5^#+1]&]  (* Harvey P. Dale, Jan 25 2011 *)

PROG

(MAGMA) [n: n in [0..1000]|IsPrime(7^n-5^n+1)]

(PARI) is(n)=ispseudoprime(7^n-5^n+1) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A155640.

Sequence in context: A060239 A127943 A012498 * A330860 A264510 A188268

Adjacent sequences:  A180742 A180743 A180744 * A180746 A180747 A180748

KEYWORD

nonn,hard,more

AUTHOR

Vincenzo Librandi, Jan 22 2011

STATUS

approved

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Last modified September 24 16:48 EDT 2021. Contains 347651 sequences. (Running on oeis4.)