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 63 is prime (see Example section).
a(23) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 29w63.
EXAMPLE
2 is in this sequence because 3*10^2 - 37 = 263 is prime.
Initial terms and associated primes:
a(1) = 2, 263;
a(2) = 3, 2963;
a(3) = 11, 299999999963;
a(4) = 15, 2999999999999963;
a(5) = 28, 29999999999999999999999999963; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[3*10^# - 37] &]
PROG
(PARI) isok(k) = isprime(3*10^k - 37); \\ Michel Marcus, Nov 15 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 15 2017
EXTENSIONS
a(22) from Robert Price, Jul 07 2018
STATUS
approved