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A289050
Numbers k such that (91*10^k + 17)/9 is prime.
0
1, 2, 4, 7, 14, 19, 20, 53, 62, 65, 68, 130, 170, 358, 449, 595, 703, 1502, 2192, 8582, 31573, 39839, 45022
OFFSET
1,2
COMMENTS
For k > 0, numbers k such that the digits 10 followed by k-1 occurrences of the digit 1 followed by the digit 3 is prime (see Example section).
a(24) > 2*10^5.
EXAMPLE
4 is in this sequence because (91*10^4 + 17)/9 = 101113 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 2, 1013;
a(3) = 4, 101113;
a(4) = 7, 101111113;
a(5) = 14, 1011111111111113; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(91*10^# + 17)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jun 22 2017
STATUS
approved