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 A127751 #5 Sep 29 2018 18:44:47 %S A127751 1,0,4,0,-4,7,0,4,-7,10,0,0,0,-10,13,0,-4,7,0,-13,16,0,0,0,0,0,-16,19, %T A127751 0,4,-7,10,0,0,-19,22,0,0,0,0,0,0,0,-22,25,0,0,0,-10,13,0,0,0,-25,28, %U A127751 0,0,0,0,0,0,0,0,0,-28,31,0,-4,7,0,-13 %N A127751 Inverse of number triangle A(n,k)=if(k<=n,if(n<=2k,1/(3n+1),0),0). %C A127751 Row sums A127752 mod 2 are conjectured to be first Feigenbaum symbolic sequence A035263. %e A127751 Triangle begins %e A127751 1; %e A127751 0, 4; %e A127751 0, -4, 7; %e A127751 0, 4, -7, 10; %e A127751 0, 0, 0, -10, 13; %e A127751 0, -4, 7, 0, -13, 16; %e A127751 0, 0, 0, 0, 0, -16, 19; %e A127751 0, 4, -7, 10, 0, 0, -19, 22; %e A127751 0, 0, 0, 0, 0, 0, 0, -22, 25; %e A127751 0, 0, 0, -10, 13, 0, 0, 0, -25, 28; %e A127751 0, 0, 0, 0, 0, 0, 0, 0, 0, -28, 31; %e A127751 0, -4, 7, 0, -13, 16, 0, 0, 0, 0, -31, 34; %e A127751 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -34, 37; %e A127751 Inverse of %e A127751 1; %e A127751 0, 1/4; %e A127751 0, 1/7, 1/7; %e A127751 0, 0, 1/10, 1/10; %e A127751 0, 0, 1/13, 1/13, 1/13; %e A127751 0, 0, 0, 1/16, 1/16, 1/16; %e A127751 0, 0, 0, 1/19, 1/19, 1/19, 1/19; %e A127751 0, 0, 0, 0, 1/22, 1/22, 1/22, 1/22; %e A127751 0, 0, 0, 0, 1/25, 1/25, 1/25, 1/25, 1/25; %e A127751 0, 0, 0, 0, 0, 1/28, 1/28, 1/28, 1/28, 1/28; %e A127751 0, 0, 0, 0, 0, 1/31, 1/31, 1/31, 1/31, 1/31, 1/31; %K A127751 sign,tabl %O A127751 0,3 %A A127751 _Paul Barry_, Jan 28 2007