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A294526
Numbers k such that (58*10^k + 419)/9 is prime.
0
0, 2, 3, 5, 6, 11, 15, 36, 38, 339, 608, 699, 1554, 3984, 4281, 7599, 12461, 13697, 13826, 16431, 39108, 43239, 46685, 103046
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 4 followed by the digits 91 is prime (see Example section).
a(25) > 2*10^5.
EXAMPLE
2 is in this sequence because (58*10^2 + 419)/9 = 691 is prime.
Initial terms and associated primes:
a(1) = 0, 53;
a(2) = 2, 691;
a(3) = 3, 6491;
a(4) = 5, 644491;
a(5) = 6, 6444491; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(58*10^# + 419)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 05 2017
EXTENSIONS
a(24) from Robert Price, May 18 2019
STATUS
approved