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A282975
Numbers k such that (134*10^k + 7)/3 is prime.
0
0, 1, 6, 13, 18, 28, 40, 45, 50, 70, 101, 210, 248, 298, 1246, 1340, 1586, 2466, 6548, 6713, 7394, 23904, 32450, 38171, 39120, 67816, 108610, 112400, 129038
OFFSET
1,3
COMMENTS
For k > 0, numbers k such that the digits 44 followed by k-1 occurrences of the digit 6 followed by the digit 9 is prime (see Example section).
a(30) > 2*10^5.
EXAMPLE
1 is in this sequence because (134*10^1 + 7)/3 = 449 is prime.
Initial terms and associated primes:
a(1) = 0, 47;
a(2) = 1, 449;
a(3) = 6, 44666669;
a(4) = 13, 446666666666669;
a(5) = 18, 44666666666666666669; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(134*10^# + 7)/3] &]
PROG
(PARI) isok(k) = isprime((134*10^k + 7)/3); \\ Michel Marcus, Feb 26 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 26 2017
EXTENSIONS
a(27)-a(29) from Robert Price, Feb 05 2020
STATUS
approved