Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
%I #14 Jun 01 2022 20:48:33
%S 1,1,1,2,5,2,3,2,6,6,3,11,18,4,5,6,13,11,15,3,6,14,6,6,61,8,2,2,3,9,
%T 48,48,21,15,6,30,3,9,6,18,6,33,30,3,60,6,24,33,33,8,71,31,11,2,5,3,
%U 24,9,16,39,19,6,9,53,60,6,26,3,16,23,17,19,44,6,131,56,8,26,9,42,12,3,24,41
%N a(n) = least k such that k*(10^n) -1 or +1, or both, is/are prime.
%H Pierre CAMI, <a href="/A102707/b102707.txt">Table of n, a(n) for n = 0..999</a>
%e for n=0 1*(10^0)+1=2 prime so a(0)=1
%e for n=1 1*(10^1)+1=11 prime so a(1)=1
%e for n=2 1*(10^2)+1=101 prime so a(2)=1
%e for n=3 2*(10^3)-1=1999 prime so a(3)=2
%t \Table[Module[{k=1},While[NoneTrue[k 10^n+{1,-1},PrimeQ],k++];k],{n,0,90}] (* _Harvey P. Dale_, Jun 01 2022 *)
%K nonn
%O 0,4
%A _Pierre CAMI_, Feb 05 2005
%E Initial term of b-file corrected by _N. J. A. Sloane_, Aug 31 2009
%E Definition clarified by _Harvey P. Dale_, Jun 01 2022