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A282278
Numbers k such that (22*10^k + 161)/3 is prime.
0
0, 1, 2, 4, 5, 6, 7, 13, 28, 36, 40, 74, 233, 425, 828, 888, 1970, 2119, 2338, 2971, 3030, 14005, 20190, 29589, 47034, 47292, 51457, 64326, 70259, 90110, 120828, 122681
OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 3 followed by the digits 87 is prime (see Example section).
a(33) > 3*10^5.
EXAMPLE
4 is in this sequence because (22*10^4 + 161)/3 = 73387 is prime.
Initial terms and associated primes:
a(1) = 0, 61;
a(2) = 1, 127;
a(3) = 2, 787;
a(4) = 4, 73387;
a(5) = 5, 733387; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(22*10^# + 161)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 10 2017
EXTENSIONS
a(31)-a(32) from Robert Price, May 04 2019
STATUS
approved