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A271377
Numbers k such that (28*10^k - 43)/3 is prime.
0
1, 2, 3, 4, 5, 6, 7, 13, 43, 112, 114, 127, 242, 247, 251, 335, 450, 616, 816, 1237, 1448, 4303, 4865, 5414, 6427, 9045, 10391, 12651, 25071, 27901, 50362, 58843, 67378, 68107, 262655
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 3 followed by the digits 19 is prime (see Example section).
a(36) > 3*10^5.
EXAMPLE
3 is in this sequence because (28*10^3 - 43)/3 = 9319 is prime.
Initial terms and associated primes:
a(1) = 1, 79;
a(2) = 2, 919;
a(3) = 3, 9319;
a(4) = 4, 93319;
a(5) = 5, 933319, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(28*10^# - 43)/3] &]
PROG
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((28*10^n - 43)/3), print1(n, ", "))); \\ Altug Alkan, Apr 05 2016
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 05 2016
EXTENSIONS
a(35) from Robert Price, Jul 02 2023
STATUS
approved