OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 3 followed by the digits 09 is prime (see Example section).
a(29) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 83w09.
EXAMPLE
2 is in this sequence because (25*10^2 - 73) / 3 = 809 is prime.
Initial terms and associated primes:
a(1) = 1, 59;
a(2) = 2, 809;
a(3) = 5, 833309;
a(4) = 6, 8333309;
a(5) = 40, 83333333333333333333333333333333333333309, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(25*10^# - 73) / 3] &]
PROG
(PARI) is(n) = ispseudoprime((25*10^n - 73) / 3); \\ Altug Alkan, Sep 20 2016
(Magma) [n: n in [0..500] | IsPrime((25*10^n - 73) div 3)]; // Vincenzo Librandi, Sep 22 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Sep 20 2016
EXTENSIONS
a(28) from Robert Price, Sep 22 2019
STATUS
approved