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A294374
Numbers k such that (44*10^k - 413)/9 is prime.
0
1, 2, 8, 9, 12, 17, 23, 26, 51, 113, 236, 509, 1659, 2769, 5258, 8456, 8787, 11487, 19367, 28094, 36114, 69663, 115697
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 8 followed by the digits 43 is prime (see Example section).
a(24) > 2*10^5.
EXAMPLE
2 is in this sequence because (44*10^2 - 413)/9 = 443 is prime.
Initial terms and associated primes:
a(1) = 1, 3;
a(2) = 2, 443;
a(3) = 8, 488888843;
a(4) = 9, 4888888843;
a(5) = 12, 4888888888843; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(44*10^# - 413)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 29 2017
EXTENSIONS
a(23) from Robert Price, Mar 03 2019
STATUS
approved