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A062573
Numbers k such that 7^k - 6^k is prime.
4
2, 3, 7, 29, 41, 67, 1327, 1399, 2027, 69371, 86689, 355039
OFFSET
1,1
COMMENTS
Terms greater than 1000 often correspond only to strong probable primes.
EXAMPLE
7^2 - 6^2 = 49 - 36 = 13, which is prime, so 2 is in the sequence.
7^3 - 6^3 = 343 - 216 = 127, which is prime, so 3 is in the sequence.
MATHEMATICA
Select[Range[100], PrimeQ[7^# - 6^#] &] (* Alonso del Arte, Sep 04 2013 *)
PROG
(PARI) is(n)=ispseudoprime(7^n-6^n) \\ Charles R Greathouse IV, Feb 20 2017
KEYWORD
nonn,hard
AUTHOR
Mike Oakes, May 18 2001, May 19 2001
EXTENSIONS
Two more terms (69371 and 86689) found by Predrag Minovic in 2004 corresponding to probable primes with 58626 and 73261 digits. - Jean-Louis Charton, Oct 06 2010
New term 355039 found by Jean-Louis Charton in May 2011 corresponding to a probable prime with 300043 digits.
STATUS
approved