OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 9 followed by the digits 51 is prime (see Example section).
a(31) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 29w51.
EXAMPLE
5 is in this sequence because 3*10^5-49 = 299951 is prime.
Initial terms and associated primes:
a(1) = 2, 251;
a(2) = 5, 299951;
a(3) = 6, 2999951;
a(4) = 10, 29999999951;
a(5) = 16, 29999999999999951, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[3*10^# - 49] &]
PROG
(PARI) is(n)=ispseudoprime(3*10^n - 49) \\ Charles R Greathouse IV, Jun 08 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jun 07 2016
EXTENSIONS
a(28)-a(29) from Robert Price, Jul 29 2018
STATUS
approved