login
A291922
Numbers k such that (2*10^k - 113)/3 is prime.
0
2, 5, 8, 13, 14, 26, 29, 263, 433, 613, 1153, 1376, 1412, 2215, 2324, 5441, 7610, 14792, 20924, 27101, 59174
OFFSET
1,1
COMMENTS
For k > 1, k-2 occurrences of the digit 6 followed by the digits 29 is prime (see Example section).
a(22) > 2*10^5.
EXAMPLE
5 is in this sequence because (2*10^5 - 113)/3 = 66629 is prime.
Initial terms and associated primes:
a(1) = 2, 29;
a(2) = 5, 66629;
a(3) = 8, 66666629;
a(4) = 13, 6666666666629;
a(5) = 14, 66666666666629; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[(2*10^# - 113)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Sep 05 2017
STATUS
approved