OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 1 followed by the digits 27 is prime (see Example section).
a(29) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 81w27.
EXAMPLE
5 is in this sequence because (73*10^5 + 143)/9 = 811127 is prime.
Initial terms and associated primes:
a(1) = 1, 97;
a(2) = 2, 827;;
a(3) = 5, 811127;
a(4) = 7, 81111127;
a(5) = 13, 81111111111127, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(73*10^# + 143)/9] &]
PROG
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((73*10^n + 143)/9), print1(n, ", "))); \\ Altug Alkan, Apr 22 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 22 2016
EXTENSIONS
a(29) from Robert Price, Jul 31 2019
STATUS
approved