OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 6 followed by the digits 29 is prime (see Example section).
a(28) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 36w29.
EXAMPLE
6 is in this sequence because (11*10^6 - 113) / 3 = 3666629 is prime.
Initial terms and associated primes:
a(1) = 4, 36629;
a(2) = 6, 3666629;
a(3) = 13, 36666666666629;
a(4) = 15, 3666666666666629;
a(5) = 23, 366666666666666666666629; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[(11*10^# - 113) / 3] &]
PROG
(PARI) is(n)=ispseudoprime((11*10^n - 113)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 05 2017
EXTENSIONS
a(28) from Robert Price, Oct 10 2018
STATUS
approved