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A295667
Numbers k such that (22*10^k + 383)/9 is prime.
0
1, 10, 16, 19, 28, 43, 76, 91, 125, 203, 283, 911, 2416, 2633, 4735, 4876, 4900, 7825, 26969, 51154, 169019
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 4 followed by the digits 87 is prime (see Example section).
a(22) > 2*10^5.
EXAMPLE
1 is in this sequence because (22*10^1 + 383)/9 = 67 is prime.
Initial terms and associated primes:
a(1) = 1, 67;
a(2) = 10, 24444444487;
a(3) = 16, 24444444444444487;
a(4) = 19, 24444444444444444487;
a(5) = 28, 24444444444444444444444444487; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(22*10^# + 383)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 25 2017
EXTENSIONS
a(21) from Robert Price, May 27 2018
STATUS
approved