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 A156826 #10 Dec 10 2016 10:32:01 %S A156826 1,2,-1,3,1,-1,4,-1,0,-1,5,2,1,0,-1,6,-2,-1,0,0,-1,7,3,-1,1,0,0,-1,8, %T A156826 -3,2,-1,0,0,0,-1,9,4,-2,-1,1,0,0,0,-1,10,-4,-2,-1,-1,0,0,0,0,-1,11,5, %U A156826 3,2,-1,1,0,0,0,0,-1,12,-5,-3,-2,-1,-1,0,0,0,0,0,-1,13,6,-3,-2,-1,-1,1,0,0 %N A156826 Square array read by antidiagonals up: same as A126988 except that the first row is A153881. %C A156826 Replace the zeros with -n/k. That is, the fraction of the row index divided by the column index with a negative sign. Then swap the element in the lower right corner with the element in the upper right corner and calculate the determinant. The result appears to be sequence A156827. %e A156826 Table begins: %e A156826 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, ... %e A156826 2, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ... %e A156826 3, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ... %e A156826 4, 2, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, ... %e A156826 5, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, ... %e A156826 6, 3, 2, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, ... %e A156826 7, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, ... %e A156826 8, 4, 0, 2, 0, 0, 0, 1, 0, 0, 0, 0, 0, ... %e A156826 9, 0, 3, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, ... %e A156826 10, 5, 0, 0, 2, 0, 0, 0, 0, 1, 0, 0, 0, ... %e A156826 11, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, ... %e A156826 12, 6, 4, 3, 0, 2, 0, 0, 0, 0, 0, 1, 0, ... %e A156826 13, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, ... %o A156826 (Excel) =rounddown(if(mod(row();column())=0;row()/column();-row()/column())*if(row()=1;column();1);0) %o A156826 (Excel) with fractions: =if(mod(row();column())=0;row()/column();-row()/column())*if(row()=1;column();1) %Y A156826 Cf. A126988, A153881, A156827. %K A156826 sign,tabl %O A156826 1,2 %A A156826 _Mats Granvik_, Feb 16 2009