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 A034840 #3 Mar 31 2012 13:22:16 %S A034840 111,123,135,147,159,210,222,234,246,258,321,333,345,357,369,420,432, %T A034840 444,456,468,531,543,555,567,579,630,642,654,666,678,741,753,765,777, %U A034840 789,840,852,864,876,888,951,963,975,987,999,1050,1062,1074,1086,1098 %N A034840 Concatenation of 3 or more numbers in arithmetic progression. %K A034840 nonn,base %O A034840 0,1 %A A034840 _Erich Friedman_