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 A306223 #6 Jan 30 2019 05:37:04 %S A306223 255,353,389,402,509,545,558,603,616,638,660,662,756,792,805,850,863, %T A306223 885,907,909,941,954,976,998,1000,1009,1031,1033,1043,1045,1049,1146, %U A306223 1182,1195,1240,1253,1275,1297,1299,1331,1344,1366,1388,1390,1399,1421,1423 %N A306223 Positions of 5's in A306211. %H A306223 Rémy Sigrist, <a href="/A306223/b306223.txt">Table of n, a(n) for n = 1..25000</a> %Y A306223 Cf. A306211, A306222, A323476. %K A306223 nonn %O A306223 1,1 %A A306223 _Rémy Sigrist_, Jan 30 2019