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A273868
Numbers k such that 10^k - 9^(k+1) is prime.
0
25, 51, 91, 107, 145, 651, 1473, 2145, 5577, 12457
OFFSET
1,1
COMMENTS
a(11) > 10^5.
EXAMPLE
25 is a term since 10^25 - 9^26 = 3538918110773326701067759, which is a prime number.
MATHEMATICA
Select[Range[21, 100000], PrimeQ[10^# - 9^(# + 1)] &]
PROG
(PARI) is(n)=ispseudoprime(10^n-9^(n+1)) \\ Charles R Greathouse IV, Jun 08 2016
KEYWORD
nonn,more
AUTHOR
Robert Price, Jun 01 2016
STATUS
approved