OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 6 followed by the digits 39 is prime (see Example section).
a(29) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 46w39.
EXAMPLE
4 is in this sequence because (14*10^4 - 83) / 3 = 46639 is prime.
Initial terms and associated primes:
a(1) = 1, 19;
a(2) = 2, 439;
a(3) = 3, 4639;
a(4) = 4, 46639;
a(5) = 6, 4666639; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(14*10^# - 83) / 3] &]
PROG
(PARI) is(n)=ispseudoprime((14*10^n - 83)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 05 2017
EXTENSIONS
a(25)-a(27) from Robert Price, Dec 23 2018
a(28) from Robert Price, Jun 17 2023
STATUS
approved