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A062594
Numbers k such that 28^k - 27^k is prime.
0
3, 5, 19, 31, 257, 773
OFFSET
1,1
COMMENTS
Terms > 1000 are often only strong pseudoprimes.
a(7) > 10^5. - Robert Price, Sep 04 2012
PROG
(PARI) is(n)=ispseudoprime(28^n-27^n) \\ Charles R Greathouse IV, Jun 13 2017
KEYWORD
nonn,hard
AUTHOR
Mike Oakes, May 18 2001, May 19 2001
STATUS
approved