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 A057050 #4 Mar 30 2012 18:57:04 %S A057050 1,3,2,6,4,1,7,3,11,6,16,10,3,15,7,21,12,2,18,7,25,13,33,20,6,28,13, %T A057050 37,21,4,30,12,40,21,1,31,10,42,20,54,31,7,43,18,56,30,3,43,15,57,28, %U A057050 72,42,11,57,25,73,40,6,56,21,73,37,91,54,16,72 %N A057050 Let R(i,j) be the rectangle with antidiagonals 1; 2,3; 4,5,6; ...; each k is an R(i(k),j(k)) and A057050(n)=j(n^2). %K A057050 nonn %O A057050 1,2 %A A057050 _Clark Kimberling_, Jul 30 2000