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A102740
Numbers k such that 7*10^k - 11 is prime.
0
1, 6, 7, 9, 10, 11, 16, 42, 53, 78, 321, 699, 1858, 3425, 4899, 5734, 11081, 11675, 12136, 14056, 16074, 77969, 158465
OFFSET
1,2
COMMENTS
a(24) > 2*10^5.
Numbers corresponding to terms <= 699 are certified primes. - Klaus Brockhaus, Feb 15 2005
For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 9 followed by the digits 89 is prime (see Example section).
EXAMPLE
Initial terms and associated primes:
a(1) = 1, 59;
a(2) = 6, 6999989;
a(3) = 7, 69999989;
a(4) = 9, 6999999989;
a(5) = 10, 69999999989; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[7*10^# - 11] &]
PROG
(PARI) is(n)=ispseudoprime(7*10^n - 11) \\ Charles R Greathouse IV, Jun 13 2017
KEYWORD
more,nonn
AUTHOR
Tom Mueller (muel4503(AT)uni-trier.de), Feb 08 2005
EXTENSIONS
a(11)-a(13) from Klaus Brockhaus, Feb 15 2005
a(14)-a(22) from Robert Price, Oct 29 2017
a(23) from Robert Price, Jun 21 2019
STATUS
approved