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 A127801 #8 Sep 30 2018 04:00:40 %S A127801 1,0,3,0,-3,3,0,3,-3,3,0,0,0,-3,3,0,-3,3,0,-3,3,0,0,0,0,0,-3,3,0,3,-3, %T A127801 3,0,0,-3,3,0,0,0,0,0,0,0,-3,3,0,0,0,-3,3,0,0,0,-3,3,0,0,0,0,0,0,0,0, %U A127801 0,-3,3,0,-3,3,0,-3,3 %N A127801 Inverse of number triangle A(n,k) = 1/(3 - 2*0^n) if k <= n <= 2k, 0 otherwise. %e A127801 Triangle begins %e A127801 1; %e A127801 0, 3; %e A127801 0, -3, 3; %e A127801 0, 3, -3, 3; %e A127801 0, 0, 0, -3, 3; %e A127801 0, -3, 3, 0, -3, 3; %e A127801 0, 0, 0, 0, 0, -3, 3; %e A127801 0, 3, -3, 3, 0, 0, -3, 3; %e A127801 0, 0, 0, 0, 0, 0, 0, -3, 3; %e A127801 0, 0, 0, -3, 3, 0, 0, 0, -3, 3; %e A127801 0, 0, 0, 0, 0, 0, 0, 0, 0, -3, 3; %e A127801 0, -3, 3, 0, -3, 3, 0, 0, 0, 0, -3, 3; %e A127801 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -3, 3; %e A127801 Inverse of triangle %e A127801 1; %e A127801 0, 1/3; %e A127801 0, 1/3, 1/3; %e A127801 0, 0, 1/3, 1/3; %e A127801 0, 0, 1/3, 1/3, 1/3; %e A127801 0, 0, 0, 1/3, 1/3, 1/3; %e A127801 0, 0, 0, 1/3, 1/3, 1/3, 1/3; %e A127801 0, 0, 0, 0, 1/3, 1/3, 1/3, 1/3; %e A127801 0, 0, 0, 0, 1/3, 1/3, 1/3, 1/3, 1/3; %e A127801 0, 0, 0, 0, 0, 1/3, 1/3, 1/3, 1/3, 1/3; %e A127801 0, 0, 0, 0, 0, 1/3, 1/3, 1/3, 1/3, 1/3, 1/3; %Y A127801 Row sums are A127802. %K A127801 sign,tabl %O A127801 0,3 %A A127801 _Paul Barry_, Jan 29 2007