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A294228
Numbers k such that (17*10^k + 43)/3 is prime.
0
1, 4, 5, 6, 7, 12, 23, 34, 160, 719, 725, 2568, 3095, 3520, 3582, 3791, 4198, 5236, 15445, 26431, 33120, 36028
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 6 followed by the digits 81 is prime (see Example section).
a(23) > 2*10^5.
EXAMPLE
4 is in this sequence because (17*10^4 + 43)/3 = 56681 is prime.
Initial terms and associated primes:
a(1) = 1, 71;
a(2) = 4, 56681;
a(3) = 5, 566681;
a(4) = 6, 5666681;
a(5) = 7, 56666681; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(17*10^# + 43)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 25 2017
STATUS
approved