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 A213223 #26 Dec 16 2024 14:27:42
%S A213223 1,20,120,1030,10040,100050,1000060,10000070,100000080,1000000090,
%T A213223 10000000100,100000000110,1000000000120,10000000000130,
%U A213223 100000000000140,1000000000000150,10000000000000160,100000000000000170,1000000000000000180,10000000000000000190,100000000000000000200
%N A213223 a(n) = 10^n + 10*n.
%H A213223 Vincenzo Librandi, <a href="/A213223/b213223.txt">Table of n, a(n) for n = 0..1000</a>
%H A213223 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (12,-21,10).
%F A213223 G.f.: (1+8*x-99*x^2)/((1-x)^2*(1-10*x)).
%F A213223 a(n) = 12*a(n-1) - 21*a(n-2) + 10*a(n-3) for n > 2.
%F A213223 E.g.f.: exp(x)*(exp(9*x) + 10*x). - _Elmo R. Oliveira_, Aug 29 2024
%t A213223 Table[(10^n + 10 n), {n, 0, 30}] (* or *) CoefficientList[Series[(1 + 8 x - 99 x^2)/((1 - x)^2 (1 - 10 x)), {x, 0, 30}], x]
%o A213223 (Magma) [10^n + 10*n: n in [0..25]];
%o A213223 (Magma) I:=[1, 20, 120]; [n le 3 select I[n] else 12*Self(n-1)-21*Self(n-2)+10*Self(n-3): n in [1..30]];
%Y A213223 Cf. A198400.
%K A213223 nonn,easy
%O A213223 0,2
%A A213223 _Vincenzo Librandi_, Mar 03 2013