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A294916
Numbers k such that (10^k + 191)/3 is prime.
0
1, 2, 3, 6, 7, 13, 18, 33, 39, 126, 154, 168, 213, 4150, 4153, 5658, 6394, 21993, 29674, 38936, 47095, 94096, 135174, 139398
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that k-2 occurrences of the digit 3 followed by the digits 97 is prime (see Example section).
a(25) > 2*10^5.
EXAMPLE
2 is in this sequence because (10^2 + 191)/3 = 97 is prime.
Initial terms and associated primes:
a(1) = 1, 67;
a(2) = 2, 97;
a(3) = 3, 397;
a(4) = 6, 333397;
a(5) = 7, 3333397; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(10^# + 191)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 10 2017
EXTENSIONS
a(23)-a(24) from Robert Price, Feb 14 2018
STATUS
approved