OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 0 followed by the digits 63 is prime (see Example section).
a(31) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 20w63.
EXAMPLE
2 is in this sequence because 2*10^2 + 63 = 263 is prime.
Initial terms and associated primes:
a(1) = 1, 83;
a(2) = 2, 263;
a(3) = 3, 2063;
a(4) = 4, 20063;
a(5) = 5, 200063; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[2*10^# + 63] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 11 2017
EXTENSIONS
a(29)-a(30) from Robert Price, May 08 2018
STATUS
approved