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 A240659 #4 Apr 15 2014 02:36:03
%S A240659 0,0,1,0,0,3,2,0,0,7,0,9,5,0,0,13,0,15,0,0,0,0,0,0,12,25,0,0,9,7,0,0,
%T A240659 17,0,37,0,13,0,0,43,0,45,0,24,49,0,0,0,0,19,0,0,6,0,4,0,67,0,23,0,0,
%U A240659 73,0,0,39,79,0,0,0,87,22,0,0,93,0,0,97,11,50,51
%N A240659 Least k such that 4^k == -1 (mod prime(n)), or 0 if no such k exists.
%C A240659 The least k, if it exists, such that prime(n) divides 4^k + 1.
%H A240659 T. D. Noe, <a href="/A240659/b240659.txt">Table of n, a(n) for n = 1..1000</a>
%F A240659 a(n) = A082654(n)/2 if A082654(n) is even, otherwise 0.
%t A240659 Table[p = Prime[n]; s = Select[Range[p/2], PowerMod[4, #, p] == p - 1 &, 1]; If[s == {}, 0, s[[1]]], {n, 100}]
%Y A240659 Cf. A082654 (order of 4 mod prime(n)).
%K A240659 nonn
%O A240659 1,6
%A A240659 _T. D. Noe_, Apr 14 2014