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.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 446w9.
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
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 26 2017
EXTENSIONS
a(27)-a(29) from Robert Price, Feb 05 2020
STATUS
approved