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A272717
Numbers k such that (65*10^k + 691)/9 is prime.
0
1, 5, 7, 17, 35, 46, 56, 148, 187, 190, 256, 551, 553, 1033, 1751, 1976, 2696, 3116, 3364, 5353, 5893, 8063, 9548, 10640, 24655, 77992
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 2 followed by the digits 99 is prime (see Example section).
a(27) > 10^5.
EXAMPLE
5 is in this sequence because (65*10^5+691)/9 = 722299 is prime.
Initial terms and associated primes:
a(1) = 1, 149;
a(2) = 5, 722299;
a(3) = 7, 72222299;
a(4) = 17, 722222222222222299;
a(5) = 35, 722222222222222222222222222222222299, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(65*10^#+691)/9] &]
PROG
(PARI) is(n)=ispseudoprime((65*10^n+691)/9) \\ Charles R Greathouse IV, Jun 13 2017
KEYWORD
nonn,more
AUTHOR
Robert Price, Aug 11 2016
STATUS
approved