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 A219876 #20 Dec 08 2018 22:02:50 %S A219876 1,2,1,1,3,3,6,7,4,1,1,5,12,19,10,20,51,44,19,6,1,1,7,27,85,155,141, %T A219876 35,70,393,580,381,146,37,8,1,1,9,48,231,780,1751,2128,1107,126,252, %U A219876 3139,8092,8135,4332,1451,344,61,10,1,1,11,75,489,2460,9331,24017 %N A219876 Duplicate of A077042 with alternating up/down antidiagonals. %K A219876 dead %O A219876 2,2