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 A228624 #15 Nov 14 2013 03:30:43
%S A228624 0,0,-1,0,1,0,0,1,1,1,0,-1,1,0,0,-1,2,3,-3,-1,0,1,-1,-2,-5,13,-7,-7,
%T A228624 -6,1,8,-1,-17,25,13,-12,11,12,-11,-12,-4,1,1,-66,-60,-26,-13,40,-67,
%U A228624 -1,82,81,-49,-32,68,103,-222,503,-39,-134
%N A228624 Determinant of the n X n matrix with (i,j)-entry equal to 1 or 0 according as i + j is a square or not.
%C A228624 Conjecture: a(n) is nonzero for any n > 21.
%C A228624 Zhi-Wei Sun also made the following similar conjecture:
%C A228624 Let A(n) be the n X n determinant with (i,j)-entry equal to 1 or 0 according as i + j is a cube or not. Then A(n) is nonzero for any n > 176.
%H A228624 Zhi-Wei Sun, <a href="/A228624/b228624.txt">Table of n, a(n) for n = 1..400</a>
%e A228624 a(1) = 0 since 1 + 1 = 2 is not a square.
%t A228624 SQ[n_]:=IntegerQ[Sqrt[n]]
%t A228624 a[n_]:=Det[Table[If[SQ[i+j]==True,1,0],{i,1,n},{j,1,n}]]
%t A228624 Table[a[n],{n,1,30}]
%o A228624 (PARI) a(n)=matdet(matrix(n,n,i,j,issquare(i+j))) \\ _Ralf Stephan_, Sep 17 2013
%Y A228624 Cf. A000290, A069191, A228591, A228557, A228559, A228615, A228616, A228623.
%K A228624 sign
%O A228624 1,17
%A A228624 _Zhi-Wei Sun_, Aug 28 2013