OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 0 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 80w51.
EXAMPLE
4 is in this sequence because 8*10^4 + 51 = 80051 is prime.
Initial terms and associated primes:
a(1) = 0, 59;
a(2) = 1, 131;
a(3) = 4, 80051;
a(4) = 6, 8000051;
a(5) = 9, 8000000051; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[8*10^# + 51] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, May 22 2017
EXTENSIONS
a(29)-a(30) from Robert Price, Aug 18 2019
Terms reordered into ascending order by Robert Price, Apr 03 2022
STATUS
approved