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A294231
Numbers k such that (56*10^k + 367)/9 is prime.
0
0, 1, 3, 6, 7, 12, 31, 33, 997, 1134, 3253, 3462, 6154, 9345, 10558, 13251, 15169, 18511, 19219, 22476, 25536, 31399, 35997, 51793, 124735
OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 2 followed by the digits 63 is prime (see Example section).
a(26) > 2*10^5.
EXAMPLE
3 is in this sequence because (56*10^3 + 367)/9 = 6263 is prime.
Initial terms and associated primes:
a(1) = 0, 47;
a(2) = 1, 103;
a(3) = 3, 6263;
a(4) = 6, 6222263;
a(5) = 7, 62222263; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(56*10^# + 367)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 25 2017
EXTENSIONS
a(25) from Robert Price, Jun 06 2019
STATUS
approved