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URL: https://oeis.org/A289943

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A289943
Numbers k such that (304*10^k - 43)/9 is prime.
0
0, 2, 3, 6, 8, 9, 12, 24, 39, 93, 99, 147, 254, 416, 510, 572, 582, 1488, 1734, 5856, 19196, 40112, 124329
OFFSET
1,2
COMMENTS
For k > 0, numbers k such that the digits 33 followed by k-1 occurrences of the digit 7 followed by the digit 3 is prime (see Example section).
a(24) > 2*10^5.
EXAMPLE
3 is in this sequence because (304*10^3 - 43)/9 = 33773 is prime.
Initial terms and associated primes:
a(1) = 0, 29;
a(2) = 2, 3373;
a(3) = 3, 33773;
a(4) = 6, 33777773;
a(5) = 8, 3377777773; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(304*10^# - 43)/9] &]
PROG
(PARI) isok(k) = isprime((304*10^k - 43)/9); \\ Michel Marcus, Jul 16 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jul 15 2017
EXTENSIONS
a(23) from Robert Price, Feb 17 2020
STATUS
approved