OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 1 followed by the digits 23 is prime (see Example section).
a(26) > 10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 81w23.
EXAMPLE
3 is in this sequence because (73*10^3+107)/9 = 8123 is prime.
Initial terms and associated primes:
a(1) = 2, 823;
a(2) = 3, 8123;
a(3) = 5, 811123;
a(4) = 6, 8111123;
a(5) = 11, 811111111123, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(73*10^#+107)/9] &]
PROG
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((73*10^n+107)/9), print1(n, ", "))); \\ Altug Alkan, Aug 11 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Aug 11 2016
STATUS
approved