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 A139900 #23 Jul 14 2019 13:53:59 %S A139900 23,47,167,263,383,503,647,743,863,887,983,1103,1223,1367,1487,1583, %T A139900 1607,1823,1847,2063,2087,2207,2423,2447,2543,2663,2687,2903,2927, %U A139900 3023,3167,3407,3527,3623,3767,3863,4007,4127,4463,4583,4703,4943 %N A139900 Duplicate of A139857. %K A139900 dead %O A139900 1,1