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A180745
Numbers k such that 7^k - 5^k + 1 is prime.
0
1, 4, 8, 140, 32060
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
No further terms k <= 100000. - Lucas A. Brown, Oct 14 2024
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
KEYWORD
nonn,hard,more
AUTHOR
Vincenzo Librandi, Jan 22 2011
EXTENSIONS
a(5) from Michael S. Branicky, Mar 31 2023
STATUS
approved