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 A090019 #11 Jan 05 2021 21:49:31
%S A090019 1,6,60,600,6000,60000,600000,6000000,60000000,600000000,6000000000,
%T A090019 60000000000,600000000000,6000000000000,60000000000000,
%U A090019 600000000000000,6000000000000000,60000000000000000,600000000000000000
%N A090019 a(n) = (3*10^n + 2*0^n)/5.
%C A090019 Fifth column of triangle A067410.
%H A090019 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (10).
%F A090019 G.f.: (1-4x)/(1-10x).
%F A090019 E.g.f.: (3*exp(10x)+2)/5 = exp(5x)(cosh(5x)+sinh(5x)/5).
%t A090019 Join[{1},NestList[10#&,6,20]] (* _Harvey P. Dale_, Apr 02 2015 *)
%K A090019 easy,nonn
%O A090019 0,2
%A A090019 _Paul Barry_, Nov 20 2003