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 83 is prime (see Example section).
a(26) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 93w83.
EXAMPLE
4 is in this sequence because (28*10^4 + 149)/3 = 93383 is prime.
Initial terms and associated primes:
a(1) = 0, 59;
a(2) = 2, 983;
a(3) = 4, 93383;
a(4) = 6, 9333383;
a(5) = 10, 93333333383; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(28*10^# + 149)/3] &]
Join[{0}, Flatten[Position[Table[100*FromDigits[PadRight[{9}, n, 3]]+83, {n, 86000}], _?PrimeQ]]+1] (* Harvey P. Dale, Nov 01 2017 *)
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 04 2017
EXTENSIONS
a(25) from Robert Price, Dec 08 2019
STATUS
approved