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A294633
Numbers k such that (76*10^k + 77)/9 is prime.
0
0, 2, 5, 9, 24, 50, 63, 98, 117, 164, 932, 1086, 3465, 5706, 6311, 6440, 8985, 10397, 14157, 23528, 100611, 144648, 164984
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 4 followed by the digits 53 is prime (see Example section).
a(24) > 2*10^5.
EXAMPLE
2 is in this sequence because (76*10^2 + 77)/9 = 853 is prime.
Initial terms and associated primes:
a(1) = 0, 17;
a(2) = 2, 853;
a(3) = 5, 844453;
a(4) = 9, 8444444453;
a(5) = 24, 8444444444444444444444453; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(76*10^# + 77)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 05 2017
EXTENSIONS
a(21)-a(23) from Robert Price, Sep 30 2019
STATUS
approved