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 A078222 #14 Jun 29 2023 18:12:08
%S A078222 2,4,8,24,48,240,480,2400,4800,24000,48000,240000,480000,2400000,
%T A078222 4800000,24000000,48000000,240000000,480000000,2400000000,4800000000,
%U A078222 24000000000,48000000000,240000000000,480000000000,2400000000000
%N A078222 a(1) = 2, a(n+1) > a(n) is the smallest multiple of a(n) using only even digits.
%C A078222 a(2n) = 24*10^(n-2), a(2n+1) = 48*10^(n-2) for n > 1.
%H A078222 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0, 10).
%F A078222 From _Chai Wah Wu_, Nov 20 2019: (Start)
%F A078222 a(n) = 10*a(n-2) for n > 5.
%F A078222 G.f.: x*(32*x^4 + 16*x^3 + 12*x^2 - 4*x - 2)/(10*x^2 - 1). (End)
%t A078222 Join[{2,4,8},Flatten[Table[{24,48}10^n,{n,0,20}]]] (* _Harvey P. Dale_, May 01 2013 *)
%Y A078222 Cf. A078221.
%K A078222 base,nonn
%O A078222 1,1
%A A078222 _Amarnath Murthy_, Nov 23 2002
%E A078222 More terms from _Sascha Kurz_, Jan 04 2003