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 A071569 #6 Mar 30 2012 18:39:02 %S A071569 0,-1,0,-2,1,0,-1,-3,3,-2,1,1,-2,3,-2,-6,5,-5,4,-2,3,-2,1,3,-3,4,-4,6, %T A071569 -7,6,-7,-9,10,-9,10,-10,9,-8,9,-5,4,-5,4,-2,2,-1,0,8,-8,8,-7,9,-10, %U A071569 10,-9,13,-12,13,-14,12,-13,14,-14,-18,19,-20,19,-17,18,-19,18,-18,17,-16,16,-14,15 %N A071569 Det(M_n) where M_n is the n X n matrix m(i,j)=1 if floor(i/j) is even, 0 otherwise. %C A071569 Det(Q_n) = 1 if Q_n denotes the n X n matrix defined by: m(i,j)=1 if floor(i/j) is odd, 0 otherwise, since this matrix is triangular with 1's on the main diagonal. %o A071569 (PARI) for(n=1,70,print1(matdet(matrix(n,n,i,j,if((-1)^(sigma(i+j))+1,1,0))),",")) %K A071569 easy,sign %O A071569 1,4 %A A071569 _Benoit Cloitre_, May 30 2002