%I A133857
%S A133857 2,25667,28807
%N A133857 Numbers n such that (18^n - 1)/17 is prime.
%C A133857 a(2) = 25667 and a(3) = 28807 found by Henri Lifchitz 09/2007.
%D A133857 H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
%H A133857 Henri & Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/
               searchform.php?form=%2818%5Ex-1%29%2F17&action=Search">PRP Records</
               a>.
%H A133857 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Repunit.html">Repunit</a>.
%e A133857 a(1) = A084740(18) = 2,
%e A133857 a(2) = A128164(18) = 25667.
%Y A133857 Cf. A128164 = Least k>2 such that (n^k-1)/(n-1) is prime. Cf. A084740 
               = Least k such that (n^k-1)/(n-1) is prime. Cf. A126589 = Numbers 
               n>1 such that prime of the form (n^k-1)/(n-1) does not exist for 
               k>2.
%Y A133857 Sequence in context: A123692 A132942 A131558 this_sequence A153912 A047076 
               A030462
%Y A133857 Adjacent sequences: A133854 A133855 A133856 this_sequence A133858 A133859 
               A133860
%K A133857 bref,hard,more,nonn
%O A133857 1,1
%A A133857 Alexander Adamchuk (alex(AT)kolmogorov.com), Sep 28 2007