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A282895
Numbers k such that (11*10^k + 91)/3 is prime.
0
1, 2, 3, 4, 5, 7, 9, 15, 27, 29, 39, 62, 77, 106, 114, 357, 555, 962, 1013, 2372, 8235, 16047, 82323, 294308
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 6 followed by the digits 97 is prime (see Example section).
a(25) > 3*10^5.
EXAMPLE
3 is in this sequence because (11*10^3 + 91)/3 = 3697 is prime.
Initial terms and associated primes:
a(1) = 1, 67;
a(2) = 2, 397;
a(3) = 3, 3697;
a(4) = 4, 36697;
a(5) = 5, 366697; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(11*10^# + 91)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 24 2017
EXTENSIONS
a(24) from Robert Price, Jul 12 2023
STATUS
approved