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A284741
Numbers k such that (29*10^k + 259)/9 is prime.
0
1, 3, 4, 6, 9, 10, 24, 27, 66, 76, 136, 346, 399, 978, 1228, 2227, 4005, 5916, 6394, 7438, 18934, 20020, 31866, 85438
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 2 followed by the digits 51 is prime (see Example section).
a(25) > 2*10^5.
EXAMPLE
3 is in this sequence because (29*10^3 + 259)/9 = 3251 is prime.
Initial terms and associated primes:
a(1) = 1, 61;
a(2) = 3, 3251;
a(3) = 4, 32251;
a(4) = 6, 3222251;
a(5) = 9, 3222222251; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(29*10^# + 259)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 01 2017
STATUS
approved