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A296093
Numbers k such that (38*10^k + 349)/9 is prime.
0
0, 2, 3, 8, 27, 30, 39, 141, 387, 626, 972, 1544, 2865, 4371, 5432, 6356, 7545, 9207, 25566, 41313, 41523, 46760, 125166, 187281
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 2 followed by the digits 61 is prime (see Example section).
a(25) > 2*10^5.
EXAMPLE
2 is in this sequence because (38*10^2 + 349)/9 = 461 is prime.
Initial terms and associated primes:
a(1) = 0, 43;
a(2) = 2, 461;
a(3) = 3, 4261;
a(4) = 8, 422222261;
a(5) = 27, 4222222222222222222222222261; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(38*10^# + 349)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Dec 04 2017
EXTENSIONS
a(23)-a(24) from Robert Price, Oct 01 2018
STATUS
approved