This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A240661 #4 Apr 15 2014 02:36:17
%S A240661 0,0,0,1,5,6,8,0,0,7,3,2,20,0,0,13,29,30,0,0,18,39,41,44,6,5,51,53,54,
%T A240661 56,63,65,68,0,0,75,78,0,0,0,89,30,0,48,7,99,0,111,113,114,116,0,10,
%U A240661 125,128,0,67,135,138,28,0,73,0,0,26,79,0,28,173,58,16
%N A240661 Least k such that 6^k == -1 (mod prime(n)), or 0 if no such k exists.
%C A240661 The least k, if it exists, such that prime(n) divides 6^k + 1.
%H A240661 T. D. Noe, <a href="/A240661/b240661.txt">Table of n, a(n) for n = 1..1000</a>
%F A240661 a(n) = A211242(n)/2 if A211242(n) is even, otherwise 0.
%t A240661 Table[p = Prime[n]; s = Select[Range[p/2], PowerMod[6, #, p] == p - 1 &, 1]; If[s == {}, 0, s[[1]]], {n, 100}]
%Y A240661 Cf. A211242 (order of 6 mod prime(n)).
%K A240661 nonn
%O A240661 1,5
%A A240661 _T. D. Noe_, Apr 14 2014