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A293825
Numbers k such that (29*10^k + 673)/9 is prime.
0
1, 2, 4, 7, 14, 19, 20, 22, 29, 40, 64, 169, 173, 1513, 2357, 3193, 4198, 11864, 18182, 19576, 31175, 38030, 57967, 122996
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 97 is prime (see Example section).
a(25) > 2*10^5.
EXAMPLE
2 is in this sequence because (29*10^2 + 673)/9 = 397 is prime.
Initial terms and associated primes:
a(1) = 1, 107;
a(2) = 2, 397;
a(3) = 4, 32297;
a(4) = 7, 32222297;
a(5) = 14, 322222222222297; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(29*10^# + 673)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 16 2017
EXTENSIONS
a(24) from Robert Price, Dec 07 2018
STATUS
approved