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URL: https://oeis.org/A293758

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A293758
Numbers k such that (7*10^k + 167)/3 is prime.
0
1, 3, 6, 7, 8, 12, 37, 44, 68, 111, 126, 142, 376, 409, 8179, 8566, 9208, 9406, 14841, 26128, 52819, 61696, 89383
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 3 followed by the digits 89 is prime (see Example section).
a(24) > 2*10^5.
EXAMPLE
3 is in this sequence because (7*10^3 + 167)/3 = 2389 is prime.
Initial terms and associated primes:
a(1) = 1, 79;
a(2) = 3, 2389;
a(3) = 6, 2333389;
a(4) = 7, 23333389;
a(5) = 8, 233333389; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(7*10^# + 167)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 15 2017
STATUS
approved