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 A050621 #24 Sep 08 2022 08:44:58
%S A050621 2,12,104,1008,10016,100032,1000064,10000128,100000256,1000000512,
%T A050621 10000001024,100000002048,1000000004096,10000000008192,
%U A050621 100000000016384,1000000000032768,10000000000065536,100000000000131072
%N A050621 Smallest n-digit number divisible by 2^n.
%C A050621 Quotients arising from this sequence give A034478 ((5^(n-1)+1)/2).
%H A050621 Vincenzo Librandi, <a href="/A050621/b050621.txt">Table of n, a(n) for n = 1..200</a>
%H A050621 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (12,-20).
%F A050621 a(n) = 10^(n-1) + 2^(n-1).
%F A050621 G.f.: Q(0) where Q(k)= 1 + 5^k/(1 - 2*x/(2*x + 5^k/Q(k+1) )); (continued fraction ). - _Sergei N. Gladkovskii_, Apr 10 2013
%F A050621 G.f.: 2*x*(1-6*x)/((1-2*x)*(1-10*x)). - _Vincenzo Librandi_, Sep 12 2014
%F A050621 a(n) = 12*a(n-1) - 20*a(n-2) for n>1. - _Vincenzo Librandi_, Sep 12 2014
%t A050621 CoefficientList[Series[2 (1 - 6 x)/((1 - 2 x) (1 - 10 x)), {x, 0, 30}], x] (* _Vincenzo Librandi_, Sep 12 2014 *)
%o A050621 (Magma) [2^(n-1)+10^(n-1): n in [1..21]]; // _Vincenzo Librandi_, Sep 12 2014
%o A050621 (PARI) a(n) = 10^(n-1) + 2^(n-1) \\ _Charles R Greathouse IV_, Jun 11 2015
%Y A050621 Cf. A035014, A034478, A050622.
%K A050621 nonn,base,easy
%O A050621 1,1
%A A050621 _Patrick De Geest_, Jun 15 1999